AITA for not choosing my sister when she split with her partner?

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The dice rolled across the table, but the real gamble was happening off the board. An 18-year-old guy, barely out of high school, found himself caught in a family tug-of-war when his sister’s relationship imploded. What started as cozy Dungeons & Dragons nights with his sister and her boyfriend turned sour when her infidelity came to light. Now, he’s holding onto a friendship with her ex, even as she pulls away, leaving him to wonder where loyalty truly lies.

Picture a cozy living room, fairy lights twinkling, and a game board littered with snacks and character sheets. It’s the kind of scene that screams connection—until tension creeps in like an uninvited guest. Readers can feel his dilemma: stick with a friend who’s done no wrong or mend things with a sister wrestling her own demons. This story dives into the messy heart of family and choices, and it’s bound to spark some heated debates.

‘AITA for not choosing my sister when she split with her partner?’

I (18M) have an older sister (28F). We only recently started to become close (past 4 years or so). Around two(?) years ago, she met this guy (23M). He made a great impression on me when we met the first two times. I thought they were a great match! They made each other happy, and I got to see my sister more than I had in a long time, which made me happy too.

I’d invited them to Dungeons & Dragons at my place, because they both seemed interested. They both agreed. Due to the ten year age gap between my sister and I, I was happy that we could finally find a hobby to mutually enjoy. However, 6 months ago I noticed that things were off.

They would come over looking stressed and dejected, and sometimes it would seem like my sister would text Boyfriend and he would deflate. I didn’t want to bring it up because, again, not really my business. But it began to get to a point where everyone at the table could see the conflict (which wasn’t hidden very well, but I thought I may just be over-analyzing things).

So at some point, I go over to their apartment. My sister wasn’t there, but me and her partner had hung out together plenty before so I wasn’t bothered. After we chilled for an hour or two, I finally asked him what was going on. I told him he didn’t have to tell me anything, that it wasn’t my problem and if he was uncomfortable then I’d leave it be and forget it.

But to my surprise, he was very open. He told me that my sister had cheated on him (emotionally and physically) with more than 3 other men, then tried to blame it on her mental health or suddenly being polyamorous. He expressed to me how I should ask her for her side as well. I told him I’d like proof to confirm the accusations. There was more than enough.

The rest of the hangout went by without any issues. The ex boyfriend still comes to d&d, and we have a great time! We talk often, and have a normal friendship. I’d never asked for my sister’s side because she was very unstable at the time, and I was scared that she would blow up on me.

We had a conversation where I told her I didn’t not want to fight or argue with her, and that I still loved her unconditionally. I told her that while, yes, my perspective had changed, that didn’t lessen my love for her. She explained to me that she felt like their intimacy had gotten stale (which was none of my business to begin with, and I did not press her for information about that).

And said that she was “intimidated” to speak with him about it because nothing changed when she did. I could understand both points, because he worked long shifts nearly every day. She told me that she felt like I was “enjoying” her ex boyfriend more than her. I told her that I would not lie to her, and that I would continue hanging out with said ex. She then told me that she would be distancing herself from me while he was still in my life.

Family drama over a breakup can feel like navigating a maze with no exit. This young man’s choice to stay friends with his sister’s ex after her cheating puts him in a tricky spot. He’s trying to honor a bond built on shared interests, but his sister sees it as betrayal. Her decision to distance herself reflects hurt, while his refusal to cut ties shows a stubborn streak of fairness.

Cheating often ripples beyond the couple. A 2022 study by the Institute for Family Studies found that infidelity can strain sibling relationships, with 34% of siblings reporting tension when one takes sides (source: IFS). Here, the brother’s neutrality—loving his sister but keeping her ex close—highlights a broader issue: how do we balance personal values with family expectations?

Psychologist Dr. John Gottman, known for relationship research, says, “Trust is built in small moments of honesty” (source: Gottman Institute). The brother’s honesty with his sister about his friendship choice is a step toward clarity, but her pain suggests trust needs rebuilding.

His maturity shines, yet he’s learning that fairness doesn’t always feel fair to everyone. What’s next? He could invite open talks with his sister, maybe over coffee, to hear her fears without judgment.

These are the responses from Reddit users:

Reddit brought its A-game with opinions that range from fist-bumps to raised eyebrows. Here’s what the crowd had to say:

TrickSea_239 − NTA. Doesn't sound like you

If he finds this support through the D&D group, then it's nice of you to let him carry on coming round. If he works long hours, he probably looks forward to this interaction. Your sister can get her interaction in the various men she's sleeping with.. Sounds like a tame FAFO to me.

Fragrant_Rope403 − NTA.. You handled that quite maturely for an 18yo. She will come around.

Corfe-Castle − NTA. Sis was cheating because she was bored of the intimacy. The ex didn’t cheat and you have things in common. I’m guessing she’s feeling isolated and guilty seeing you both hang out

SheepPup − NTA. I wanna rephrase this whole thing more succinctly “my sister is mad that I didn’t stop talking to her boyfriend, who is my friend, after she cheated on him. Am I the a**hole?” No. No you are not.

P35HighPower − The most interesting thing about this is that being the youngest at 18 you are the one acting in the most mature manner.. Well done and no, NTA.

YearOneTeach − NAH. If you want to be friends with him you can, but you also have to accept that it’s completely fair for your sister to distance herself from you as a result. Most people do not want to remain that close to their exes, and if you are remaining friends with him and involving him in D&D it makes sense that she would want to take a step back and no longer be a part of those things.

I’m kind of curious why you haven’t asked for her side, or at the very least tried to talk to her about the underlying issues. It kind of seems like you know she’s struggling mentally. Do you know if she has sought help? Is she in therapy?

KindBoysenberry7333 − NTA that being said I have seen first hand familiar relationships go up in flames by people choosing to still be friends with their family’s exes. So while you are allowed to be friends with whoever you want I would recommend thinking about potential consequences and whether or not you are willing to live with them. Again NTA but it is defiantly something to consider.

Mrs_Gracie2001 − You never asked her? How do you know you got the whole story?

LibraryMegan − NAH It’s definitely weird to keep hanging out with your sister’s ex after they broke up, regardless of how they broke up. You have to decide which relationship is more important to you, because she is distancing you over it.

OldSignificance2039 − I think you need to ask yourself: if the shoe were on the other foot, would you want to see your ex hanging out with your sister all the time? The answer would likely be a hard no. This situation isn’t just about the guy or the cheating, as that doesn’t involve you.

It also raises questions about the relationship between you and your sister. I wonder if your ex wants to remain friends with you in hopes of getting back together or hurting her through you. Additionally, it might be helpful to give it some time. The loss of a relationship can feel like an open wound. I wish you and everyone involved the best.
These takes are lively, but do they nail the whole story? Maybe there’s a twist or two worth pondering.

This young man’s story is a reminder that family ties can bend without breaking—but it’s no walk in the park. Choosing friendship over taking sides cost him closeness with his sister, yet his heart stays open. What would you do if your sibling’s breakup put you in the hot seat? Toss your thoughts into the mix and let’s see where this dragon-slaying quest leads.

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