My older brother (19) recently got a new girlfriend, Lily. We were having a family game night and me and my older sister were both bringing our partners, so he brought his.

Everything was going fine, she just seemed to have an odd personality, but whatever. Until the games were mainly over. I was sitting in the front room with my girlfriend watching a movie. She fell asleep on my lap after a while and I let her sleep. Everyone else was in the back room playing charades or something.

Around halfway through the movie Lily walks in and starts SCREAMING about how my girlfriend had stolen her seat and amongst other things, ruined her life. I was a bit groggy and was mainly like, what the fuck. My girlfriend woke up, very confused. Lily then drags my girlfriend off the chair and sits down to watch die hard with me. I asked her what the hell she thought she was doing.

All she said was "claiming what's mine." I get up, help my girlfriend and go into the back room to ask what the hell that was. My brother just says that she gets like this and will be back to normal in a minute.

Lily walks in like nothing happened and sits on a beanbag.

I ask her again and this time she says that "I sat in that seat last time so I own it an can do whatever I want."

I tell her to apologise. And then she goes on a rant about how no-one loves her and how she misses her grandparents and how she just wants to be understood.

My brother starts comforting her and I basically just told her to grow the duck up and learn that nobody gives a shit that she is a psycho and that she'll just get fired or whatever.

Now he only people in that room who haven't blocked me are my girlfriend and my dad and sister.

Am I the asshole?