My parents divorced when I (15m) was 4. My memory of them together is really fuzzy and the normal to me is mom's house, dad's house. Mom's house always felt more like home to me though. But we live with my grandparents so maybe that's why and I always loved living with my grandparents. I'm really close to them. I never hated going to my dad's house though and we were close until Covid stuff happened.
My dad introduced me to his girlfriend in December 2020 and they got married in May 2021. She has three kids. Her oldest is 10, her middle kid is 7 and her youngest is 5. The youngest is a boy and the other two are girls.
When we all moved in together me and her oldest got our own rooms and the younger two shared. A few months ago my dad and his wife were really annoyed because the 7 year old hates sharing with the 5 year old. They don't get along at all (neither do the girls) and the 7 year old doesn't like how clingy the 5 year old is, and he really is clingy. He gets nightmares and wants to share a bed and all kinds of stuff. But not with the adults. With his sister but he also asked me a few times. Because the girls don't get along and because the 10 year old is a girl who is at an age where sharing with a brother might be awkward, my dad told me he wanted me and his stepson to share and he laid out the expectation that I be there for my stepbrother for nightmares and stuff and to really invest in being a good brother because he's far more affectionate and longing for closeness that neither of his sisters give him. I told dad I wasn't okay with any of that and I didn't want to share a room with his stepson and be responsible for a closeness I don't want. He told me I had no choice and that I should want a closeness because we're family and I have the chance to have a brother. The rest of that week he was in my (former) room and he tried climbing into my bed every night and he would wake up once I went to bed (really light sleeper) and would chat my ear off.
Two years ago I was given the choice to stay at either parents house more permanently and with the changes at dads, I decided to stay with my mom and not go to my dad's for parenting time anymore. Dad didn't like it but he thought I'd come back around. I still haven't been there since. My dad's wife is furious because her son hates being on his own in the room all the time. She berated me real bad for that and mom told her to never contact me again when she heard it. My dad told me I need to stop acting like this and I came across and very entitled and selfish.
AITA?