AITAH for cutting off my family after my brother cheated on his wife and got his mistress pregnant?

Under the weight of long-buried resentments and toxic family dynamics, a fateful secret finally exploded into the open. The familiar comforts of childhood were replaced by painful memories of favoritism, abuse, and betrayal. In the midst of these turbulent emotions, the OP found herself forced to choose between silence and accountability.

Now, with her brother’s affair and his mistress’s shocking pregnancy upending their already fractured family, the decision to cut off toxic relatives became unavoidable. Determined to protect her sister-in-law and preserve her own well-being, she draws a firm boundary, setting the stage for a family drama that questions the very meaning of loyalty and justice.

‘AITAH for cutting off my family after my brother cheated on his wife and got his mistress pregnant?’

Oh boy this is going to be long. I will try my best to be concise. Also, sorry if formatting is weird I'm on mobile. Okay, so some backstory, my brother (35M), is the favorite child. My mother (55F) always took more photos of him, always went to his games/plays/events/etc but never any others.

If he got in trouble for anything, for example fighting at school and getting suspended, his punishments never lasted more than an hour. Meanwhile I, (31F) would be screamed at, cussed at, hit with shoes/belts/spoons if I so much as breathed the wrong way.

He has been married to his wife (35F) for 18 years. I love my SIL more than anything. She is sweet, funny, kind, and always the first to help when you're in need. Her biggest downside has always been that she isn't very money smart but my brother is and I thought they worked well together when it came to balancing each other.

They bought a house, got a dog, and were trying to have a baby all while still saving a significant amount. My brother says they started fighting a lot cause he wanted to save money and do IVF but my SIL really wanted a baby without all that.

Admittedly, while they never struggled to get pregnant their babies were never healthy enough to survive after birth and their last 3 pregnancies ended with infant loss. Well, he got her pregnant again anyways and the baby is perfectly healthy. The day she told my brother she is pregnant he asked for a divorce and confessed he cheated with a co-worker (23F).

The biggest reason why I am so angry about this isn't because of how much love I have for my SIL but more so because my brother claims that he didn't know he even wanted a divorce until he cheated on his wife and realized he didn't feel guilty about it. But he also has confessed to our mother that he actively pursued a relationship with his co-worker.

His co-worker is also very aware that he is married and has even met his wife. In fact, she regularly shops at the store that my sister-in-law works at and had made it a point to approach her at work prior to my SIL finding out about the affair. Now on to what caused me cut off my family, I went to visit my SIL for the first time in a while.

She was giving me a coffee table as her and my brother are selling their house (they are not divorcing, my brother will not file) and I decided I would also visit with her. Just to see how she was doing, check on her pregnancy and just all around, make sure that she is okay.

Towards the end of my visit, my brother and my mother both started calling me excessively, texting me that I had to call them back right now and I hadn't even left her house yet. Once we got in the car and started driving away. My brother and mother started calling again. Several times back-to-back, and we finally answered And that's when they started getting angry at me.

Apparently my SIL told my brother she didn't want to go shopping after their 20 week appointment the next day and my brother thought it was my fault. My SIL does not know that my brother's mistress is pregnant and that they are only 4 weeks apart. He assumed I told her and when I responded that I had not told her anything he called me a liar and screamed and cursed at me.

I ended up yelling back and told him to

I ended up blocking them both. My mother got so angry she couldn't get a hold of me she demanded I get my own insurance on my car (she bought it for me and is the only person on the title, it is still being financed by the dealership. I pay the car payment directly and send her money for the insurance), and that I add her back to Life360 so she knew where HER car was at all times.

She also said my BF (30M) is not allowed to drive it (he doesn't unless I'm in the car with him). She texted my boyfriend all of that since she couldn't get to me. I ended up taking the car to her house and dropped it off with the keys and told her to do what she wants with it since she wanted to know where it was at all times.

She ended up texting my BF that we are both

This whole time my mother has been hosting my brother's mistress at her house after my brother moved in with her and she keeps protecting him as much as she can. She even gaslights my SIL to make her think the divorce and affair are her fault. And she tries to blame me for my brother and SIL 'fighting'. I am so tempted to go nuclear.

With everything going on I could get my brother, mother, and the mistress fired from their jobs and could even get my parents evicted from their home since they live in a 55+ community and my brother is not on the lease. His staying there goes against their lease agreement and they could be evicted if the landlords/property management company finds out.

I won't get them evicted or my mother fired but I wonder if my brother and his mistress should suffer consequences especially since my brother is the mistresses direct supervisor. I also wonder if IATAH for cutting everyone except my SIL off after all of this. I tried to stay neutral for as long as I could because my SIL didn't want to cause fighting but I can't bring myself to stay quiet anymore.

My mother and brother think I'm pretty much evil at this point because I won't protect my brother anymore. I also wonder if IWBTAH if I told my SIL about the mistress being pregnant and regularly staying with my brother at my mother's house.

I know she would be angry enough to get a lawyer involved and I would support her 100%. So Reddit, what do you think? AITAH? Should I tell my SIL? And should I go nuclear? Tldr: Brother cheated on wife and got mistress pregnant. Brother and mother started fighting with me and harassing me over calls and texts so I went nocontact and returned my car.

When family members engage in behavior that undermines trust and upends long-established bonds, setting boundaries can be a necessary—and painful—act of self-preservation. Relationship expert Dr. John Gottman advises, “When family dynamics become toxic, setting clear boundaries is essential for protecting your mental and emotional wellbeing.” This perspective reminds us that ending ties with destructive family members is sometimes a vital step toward healing.

In this complex scenario, the OP’s decision to cut off her brother, mother, and the mistress reflects a refusal to remain complicit in patterns of abuse and deception. By refusing to enable toxic behavior—whether through financial support or continued emotional entanglement—she is taking responsibility for her own mental health. Research on dysfunctional family systems shows that enforcing personal limits is often crucial for stopping the cycle of blame and enabling healthier relationships.

Moreover, the decision to protect her sister-in-law by planning to reveal the truth is consistent with a commitment to accountability and transparency. Such actions, though potentially disruptive, echo the advice of many experts in family psychology: honesty and boundary-setting can pave the way for meaningful recovery even amid chaos.

Heres what people had to say to OP:

Here are some hot takes from the Reddit community—raw, unfiltered, and laced with both humor and truth.

RubyMariigoldd − you’re not the a**hole for cutting off toxic family who expect blind loyalty while enabling cruelty. Here’s what you should do, tell your SIL the truth so she can protect herself, and let the rest deal with the fallout of their own choices.

trayC-lou − GO NUCLEAR. Being nice don’t get you s**t, staying neutral didn’t get you anything but a barrage of s**t & getting called a liar. F**k the lot of them they’ll paint you as the bad guy regardless so might aswell f**k s**t up in the process & no don’t pay her for that car if she is using it to threaten you, it’s all in her name so her responsibility, she could’ve left the car out of it because you pay her but again she didn’t. F**k them all 💥

WinterFront1431 − Tell SIL he got someone else pregnant so she can prepare and act accordingly.. I'd also refuse to pay for the car and have it get towed.

Orsombre − Protect your SIL and your nibling to be. But before going nuclear, gather as much evidence as you can against your brother, so that he pays for child support or lose his job with your evidence. His choice.

United-Manner20 − NTA but you need to tell your sister-in-law. The other woman’s gonna have a child as well within a month of hers. She’s going to find out knowing now is gonna be much better than when she is on her own with a newborn. I would cut all of them off except for your sister-in-law. And I would tell her the truth. I would also contact your parents community and let them know your brother is living there.

Your family made their decisions. They were selfish and wrong and their act have consequences. They are no longer your issue. She likely only purchased that vehicle for you as a means of control and now you can’t do it back. She no longer has that I doubt she watches the car out of the kindness of her heart

Lonely-World-981 − \ If he got in trouble for anything, for example fighting at school and getting suspended, his punishments never lasted more than an hour. Meanwhile I, (31F) would be screamed at, cussed at, hit with shoes/belts/spoons if I so much as breathed the wrong way..

The Golden Child / Disfavored Child dynamic is common to families with Cluster-B Personality Disorder parents.. Your mom sounds like she has BPD.. Check out r/raisedbyborderlines and r/raisedbynarcissists. As crazy as this sounds, you're not alone in any of this. This is unfortunately common. Check out those subs.

iknowsomethings2 − NTA. You should tell your SIL everything, she should make an appointment with the lawyer and also get everything sorted before her child arrives. F**k your brother and mother, they’re both POS’s, and DO NOT pay for a car you are not using.

They sound toxic and manipulative.. Also, don’t get your brother fired until divorce settlement is sorted and any alimony / child support. F**k your mums lease though, when the divorce is sorted or your SIL has moved out, then you rat her out as you don’t want your brother moving his mistress into their house.

primordial_chaos_007 − OP, your family's selfishness has gone off long enough and now they've got multiple innocent lives in the crossfire (SIL, her pregnancy). If I were you, I wouldn't go nuclear. I would go quasar. Sometimes it's okay to scorch earth for those who can't manage to stand up for themselves. NTA, but listen to your inner Hecate and unleash her on your toxic family

Shade_Hills − Wait i didn’t even CATCH that SIL was also pregnant. That poor woman. Can you house her? Im not sure she needs it but just in case

Effective-Hour8642 − Don't make the payments, you don't have the car. Personally, I'd tell HR about the affair and your SIL about the pregnancy. She's going to find out and I think it might be easier coming from you, while you're there with her.. Someone else mentioned if you could house her. Would that be a possibility?. Your brother sucks. What a mess.. Take care.

The comments reflect a fierce consensus: many believe that cutting off toxic family members is a justified move, and that the OP’s plan to warn her sister-in-law is both necessary and courageous. As opinions vary, one thing is clear—no matter how messy family ties become, truth and self-respect should never be compromised.

In the end, the decision to sever ties with toxic family members is a deeply personal one—often born out of long-standing pain and a desire for a healthier future. While the OP’s choices may seem drastic, they underscore the importance of accountability and self-care in the face of betrayal. What do you think: Is cutting off toxic relatives the only way to heal, or can forgiveness sometimes lead to restoration? Share your thoughts and experiences below—your insights might help others navigating similarly turbulent familial waters.

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