AITA for excluding my stepsister from my birthday sleepover and moving in with my dad?

I'm 17F, split time between my parents, and I asked to live with my dad but backed off to avoid conflict—now my mom's new wife's daughter was forced into my friend group and I finally snapped after my birthday.

My parents split when I was 11 and I alternate weeks between them. I prefer living with my dad, but when I tried to make the switch my mom made a big deal so I dropped it to keep the peace. My mom married Dan this year; he has two kids who live with him full time: Amy (15F) and Tye (12M). I get along okay with Tye, but Amy is constantly intrusive—loud, rude, and crossing boundaries. We share a room while the basement is being fixed, so I can't escape her when I'm at my mom's place. Both Dan's kids are autistic, but Amy's behaviour is on a different level: yelling, picking fights, and sometimes breaking or taking my things.

I'm a 17-year-old who avoided drama for years, but when Amy ruined my birthday sleepover vibe I decided to stop putting up with it—and I moved in with my dad after telling my mom I wasn't coming back.

Amy's parents (my mom and stepdad Dan) have been trying to insert her into my friend group for years. At first it was small—asking me to bring her along—but it escalated when Amy cried about being left out at school. Now my mom expects me to include Amy in everything on mom's weeks. My friends have made it clear they don't want Amy around because of how she acts; so to avoid drama, I stopped bringing friends over to my mom's house and I mostly wait until I'm back with my dad to hang out.

"I don't think I should have to blow up my social life just because she can't be normal."

For my 17th birthday I told my mom I only wanted a quiet family dinner instead of a sleepover at her place because I knew Amy would ruin the vibe. I scheduled my friends' sleepover for the following weekend at my dad's, where it's always been easy and relaxed. The sleepover went great, but Amy saw a group photo a friend posted and got upset she wasn't invited. My mom and Dan are furious, saying I should include Amy and "help her out" now that we're family. I feel guilty for excluding her but also resentful—I've been expected to tolerate behaviour that's hurtful and boundary-crossing for years.

"I know other autistic people — this isn't 'normal' weird; she's yelling, breaking things, picking fights."

After talking with my dad, he said if it's that bad he supports me choosing where I live. I packed my things into a backpack and stayed at my dad's after school instead of going back to my mom's. When my mom called furious, I told her I was staying with my dad and hung up when she yelled. My dad is on the phone with my mom and Dan right now arguing about it. I feel bad my dad is getting heat, but I also feel relieved—no more weekly packing or stolen stuff. If my mom won't respect boundaries, I might limit contact further once I'm in college.

🏠 The Aftermath

I'm currently staying with my dad and have told my mom I'm not coming back to her house. My dad supports me and has spoken to my mom, which has escalated tensions at home. My mom and Dan feel I'm being cruel to Amy; I feel like my boundaries were ignored for years.

At my mom's house: hurt feelings, anger, and an argument about fairness and inclusion. At my dad's house: relief, more stable routine, and no risk of my things being taken or my space invaded.

Practical consequences: I packed light and kept most things at my dad's, so switching permanently is easier; emotionally, my relationship with my mom is strained and there's ongoing conflict about whether I should be forced to include Amy.

"I packed a backpack and chose my mental health over constant chaos."

I feel relief and guilt at the same time—relief to be away from the stress, guilt that my dad is taking flak and that Amy is lonely. But I've also reached my limit after years of being expected to accommodate behaviour that harms my friendships and privacy.

💭 Emotional Reflection

This conflict isn't just about being "mean" to a lonely kid—it's about personal boundaries, safety, and respect. The OP tolerated a lot to keep peace, but inclusion shouldn't come at the cost of repeated bullying, theft, or emotional harm.

On the other hand, Amy is clearly struggling and lonely, and parents understandably want to help. The real issue is that help has been implemented by forcing the OP into harmful interactions instead of seeking supports that actually teach Amy social skills or manage behaviour in ways that don't punish others.

A fair approach would include setting clear expectations, getting professional support for Amy's behaviour, and parents accepting that their child's needs might require changes that don't involve pressuring a teenager into constant accommodation.

Here’s how the community might see it:

“You’re allowed to protect your mental health—forcing a teen into constant stressful social situations isn’t the same as helping.”

“Parents should get Amy support instead of making her a permanent guest at someone else's social life.”

“Your mom offering without a conversation was the tipping point—communication and boundaries came too late.”

Responses split between empathy for Amy's loneliness and backing the OP's right to boundaries; many suggest therapy, structured social coaching for Amy, and clearer parental limits rather than forcing the friend group to adapt.

🌱 Final Thoughts

No one wins when a teenager's social life is sacrificed to manage another child's behaviour. The OP reached a limit after repeated boundary violations, and moving in with her dad was a practical step to protect herself.

That doesn't erase Amy's needs, but it does highlight that helping her shouldn't come at the expense of someone else's safety and friendships. Parents choose easier emotional fixes—forcing inclusion—over harder work like therapy, behaviour plans, or supervised social skills practice.

What do you think?
Is the OP justified in refusing to include Amy and in staying with her dad, or should she have tried harder to make room? Share your thoughts below 👇