Why don't my boyfriend ever ask me to chill with him and his buddies?

okay im really starting to get pissed off over this situation.he has been my boyfriend for 3 months and i have started to notice something.he love to go out with his friends and when i ask if i can go chill with him and his friends when they are planning to go somewhere fun.he doesnt let me >_< he'll always think of some sort of excuse. okay i understand that my bf need a fun time alone with his buds but it's everyday.we go hangout when he feels like it >__< .im not one of those girls that always need their bf around them allll the timme just to let u know . and there is another thing that really annoys me. I KNOW his friends! every single one of them! alex, micheal, kevin, wildany, ryan, tomasz, robert, andre and alot more! i have talked to them before and they think im cool and everything(and one of them has a crush on me,lol).sooo i really have no idea whats the problem is :/