Me and my stepsister are 16 and we’re in the same grade in high school and share a couple of classes. We had an overnight field trip a month ago and she had nobody to room with. I’d made plans to share with my friends weeks in advance and then my stepsister asked me a week before. I told her I’d already made plans with my friends.

The day of the field trip she still had nobody and there was a huge fuss made out of rooming with her. She asked me again and had our teacher asked but I’d already figured out my plans. She ended up with someone else and that girl snuck out to her friends and left my stepsister in the room on her own.

When my mom found out she was angry at me for not being my stepsister’s roommate. She told me I knew my stepsister had nobody and I told mom it wasn’t my fault or problem that my stepsister doesn’t have friends. My mom said we’re sisters and I could’ve made it a fun sisterly night if I’d said yes and instead I made my stepsister feel like shit.

Mom told me it wasn’t fair to hate my stepsister for spending time with her. And she said she knows that’s what it’s about. She said the fact I complained to her five times about it tells her that this was a way for me to get revenge or to humiliate her and it makes mom want to spend no time with me. I told mom she never spends time with just me anymore anyway so what does that change.

My mom’s not wrong about the reason I don’t like and even hate my stepsister. When my mom first married my stepsister’s dad it was fine. But two years into their marriage my mom made all kinds of excuses not to do stuff with just me but she could still find time for stuff with just my stepsister. Before that she could do it with both of us. When I do spend time with my mom it’s when all of us are together and she’s on my case about not being sisterly or bffs with my stepsister. Me and mom fight about this stuff. She told me I should love my “sister” and I have always said my stepsister isn’t my real sister and she’s not my friend either. Any social issues she has are not on me to deal with and I feel stronger about this because my mom makes time for her but not me. When I told my mom I had an issue with her spending time with just my stepsister when she makes excuses about not spending time with me, she always says I had her for longer and if she has limited time she should use it on the person who got less overall.

The only time me and my stepsister talked about that issue is when she told me she wasn’t giving up time with my mom for me and that it’s not her fault mom hasn’t enough for me. I told her in response that I don’t care if she wants to be friends or sisters.

My mom and her husband have been married for 6 years now. So two years of things being normal and four like this.

So AITA?