My boyfriend and I have been together one year on February 16th. We've been fighting quite a bit lately. One thing mainly and just need a little advice on that.

He offered to go to prom with his friend if she doesn't have a date to prom this year. Our prom isn't until next year but I really want his first prom to be with his girlfriend (me). It just upsets me that i'm going to be sitting at home waiting for him to get home from prom with another girl and there's going to be pictures of them everywhere, he will do his first walk through with her, first prom dance with her and i'll just be home waiting. even if i go out with friends, that is all I'll be thinking about it the whole time. I've never even met this girl but she's his best friend. During a fight about it I asked which one he cares about more, hers or the one he gets to attend with me and he said hers. He can't understand why I'm mad, and I just need to know if i'm being unreasonable or dramatic and what anyone else would do here?