Why doesn’t my boyfriend invite me to go out with him?

My bf is in a grad school program for screenwriting and there’s only like 8 people in his class but they always go out to a bar after and drink and there’s a girl that is also his classmate that goes with him and the 7 other guys. I told him I want to meet his friends one day and he just said “oh yeah maybe on a weekend we can all hang out” (since his class is on Tuesdays and gets out at 10) he also told me the girl that goes out with them called him “doll face” the other night when they went out. I don’t think he’s cheating on me but why else would he never invite me to go out with them? His excuse is always “oh well it’s kinda late when we go out and it’s a 25 min drive from your place” Thoughts??