AITA for moving in with my dad’s “affair baby”, ie my sister, and not asking her to leave or hide in her room so my mom can visit without seeing her?

In a cozy apartment filled with laughter and sisterly banter, two young women built a home together, their bond defying a painful family secret. For one Reddit user, moving in with her half-sister—the child of her father’s affair—was a joyful step, but it stirred old wounds for her mother.

Expecting the sister to vanish during visits, the mother’s hurt clashed with the daughter’s loyalty to her newfound sibling. What seemed like a simple roommate decision spiraled into a test of boundaries and forgiveness. This heartfelt story pulls readers into a tangle of love, betrayal, and family ties, asking: can a daughter honor her sister without dishonoring her mom?

‘AITA for moving in with my dad’s “affair baby”, ie my sister, and not asking her to leave or hide in her room so my mom can visit without seeing her?’

When I was 14 I found out my dad stepped out on my mom and got another woman pregnant when I was a baby, so I have a half sister I'd never met. My mom found out when she realized he was making child support payments, and she kicked him out for a few weeks but she eventually forgave him on the condition that he never contact the 'affair baby' (her words) and she never has to hear about or see her.

I'd grown up the youngest of the family with 4 older brothers so little 14yo me was just excited to have a) a sister and b) a younger sister at that. I begged my dad to get me in contact with her and eventually he gave me her name so I could look her up on social media.

Turns out she knew already she had half siblings, her mom was pretty open with her about the situation, and she had always been pretty curious to know us, so she was happy to be in contact with me. I gave my mom a heads up that I was talking to my half sister and she was obviously very unhappy about it and said she just didn't want to know about it.

My half sister and I became really close, I didn't tell my mom about it, it was weird but we made it work. Fast forward 6 years and both me and my half sister were starting to think about moving out of home. We both felt like the most obvious thing to do was get an apartment together,

since we both needed a housemate at the same time in the same area, and we were so close, but with my mom's issues with her we weren't sure. Eventually I just bit the bullet and asked my mom how she'd feel if I moved in with my half sister. Again she was obviously not thrilled about it but said she'd be fine with it as long as she doesn't have to see or hear anything about my sister.

I took that to mean if I wanted to spend time with my mom I'd just go visit home or we'd go out somewhere together. After we moved in, I found out my mom meant she wanted to come visit me sometimes and she wanted me to either have my sister leave or hide in her room for that time. She's acting like I should have known that without her telling me,

and she's upset with me that I refuse to kick my sister out of her own apartment or make her hide like Harry Potter, 'I'll be in my room, making no noise, and pretending I don't exist'. It turns out she's also mad at me for moving in with her in the first place, apparently I was supposed to know that when she insisted she'd be fine with it, she actually wanted me to not do it.

Family secrets can cast long shadows, and this Reddit user’s story illuminates the fallout. By choosing to live with her half-sister, she embraced a bond her mother sought to erase, creating friction. The mother’s demand to hide the sister reflects unresolved pain from her husband’s betrayal, unfairly aimed at an innocent child.

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Dr. Susan Heitler, a family therapist, notes, “Blaming a child for a parent’s infidelity displaces anger and delays healing”. Studies show 50% of spouses struggle with trust post-affair, often projecting onto others. The mother’s insistence on erasing the sister’s presence burdens her daughter with her own unresolved grief.

This taps into broader issues of blended family dynamics and forgiveness. The user’s refusal to hide her sister honors their bond but risks alienating her mother. Therapy could help the mother process her pain separately. Meeting outside the apartment might ease visits.

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Take a look at the comments from fellow users:

Reddit rallied with fiery support for the user, tossing shade at her mother’s misplaced anger with a side of humor. Here’s the crowd’s take on this family drama:

residentcaprice − NTA. Think your mom needs marriage counseling and therapy. She 'forgave' your father but faulted his child when it wasn't her fault.. Guess she thought that by pretending the child didn't exist, her marriage isn't broken and her family remains whole.. Edit: Thank you for the silvers!

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nemc222 − NTA. My husband cheated on me and got a young woman, 10 years younger than our sons, pregnant. Our marriage ended despite his protests because it was not his first time to cheat. He ended up marrying the young female. We have a grandchild that was born two months after this child was born and they are the best of friends.

I see her at birthday parties, I hear about her through the other grandchildren, etc. I would never in a million years treat this child as if she did not exist because of a poor decision my exhusband made. Your mother’s issue should not be with this child, or even this child’s mother, it should be with your father and no one else.

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YesIDidTripAgain − NTA. Wow, your mom is acting atrociously. She is blaming a CHILD for the mistakes your father made. Somehow, your sister is the villain of this story instead of her cheating husband? You have every right to get to know your sibling and live with her and foster a relationship with her.

If your mom doesn't want to see her, then she doesn't need to come over to the home that you and your sister share. Full stop. You wouldn't bring your sister to her home and expect your mom to hide away to avoid her. Your mom is being completely unreasonable.

I think you're showing great character in embracing your sister and standing up for her. Good for you. Sister relationships can be some of the best on the planet, I'm happy you guys were able to find each other despite the parental drama.

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RecentRegister239 − NTA. Your mom is holding your sister responsible for your dad’s actions. Neither you or your sister have done anything wrong and it’s actually awesome that you’ve built a relationship. Your sister deserves to feel comfortable in her own home. If your mom is uncomfortable, she doesn’t have to visit you there.

isthisariddle − NTA Your moms issues are with your dad not your sister. She is projecting them on your sister. If she can stand to look at your dad then she can look at your sister who is innocent in this whole situation.

It seems your mom wants to pretend like your dads affair never happened, she needs to see a therapist. Pretending their isn’t a problem doesn’t solve anything.. You sound like a great sister! And daughter. You handled everything in the right way.

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MedusaYHLQMDLG85 − NTA but your mom, no offense… Is TA for making your dad cut contact and for how she has handled the whole thing. Its not a childs fault/your sisters fault how she came to be.

tatasz − NTA. Also, your sister has nothing to do with the whole thing. If your mom wants to punish someone, should be your dad and not her.. You can meet your mom outside the flat, so noone is inconvenienced.

IDKareyou77 − NTA. 'If you want to be weird, just don't visit.'

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Drops_of_Brain − NTA, but your mom sure is. Your mom needs a good dose of the phrase every parent loves until their kid drops it on them: 'My house, my rules'. If she wants to visit you, then she's going to have to grow up and act like an adult around your sister.

She's already gotten 18+ years of getting to pretend she doesn't exist. She can either act like an adult for the short periods of time she visits, and be civil, or she can not visit. Expecting everyone else to shun your sister because she's too much of an immature brat to deal with her problems, is a no go.

NewRedSpyder − NTA. I get that your half-sister is a living reminder of what your father did to her, but she’s being super petty and controlling by not wanting you to interact with her. If she doesn’t want to interact with your half-sister because it reminds her of what your dad did to her than that’s fine, but she has no right to make it so you can’t.

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Reddit’s got her back, but are they seeing the full picture of this tangled family web?

This Reddit user’s choice to live with her half-sister has cracked open old wounds, pitting her loyalty to a sibling against her mother’s pain. Refusing to hide her sister, she’s drawn a line, but at what cost? Is she right to stand firm, or should she bend for her mom’s sake? Share your thoughts—how would you navigate a family divided by a parent’s past mistakes?

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