Aita for being "jealous" over my best friend?

So my friend (f14) mia has a boy bestfriend (m17) we'll call him alex, and they were a couple back in the summer, but broke up because he was a jerk. So a few days ago he apologized and thry started talking and stuff. The thing is, everytime me and her walk together in school, he just.. grabs her hand and drags her away with him (??) and so naturally, of course i would be annoyed. And on her birthday we were supposed to stay at the mall for an extra hour and a half after all the people she invited left, but alex told her if he could stay and make one of the invited ones stay too and they could watch a movie. He didn't mention me. She said okay and was telling me about it and told me if i wanted to stay with them. I said okay. I don't want to be the jealous best friend because i am not and i just want someone else's opinion on this as I don't want to be the jerk and control what she does because i am genuinely happy for her but i just don't know what to do and I don't have anyone to talk about this, as all my friends just laugh because no one likes the guy.