Boyfriend has girls that are his friends?

i've been with this guy 4 2 years and he was these girls he would always hangout with & have the same classes with, they were never so close till this summer. now they want to do gettys & i asked him to take me because i would feel comfortable, but he told me that he doesn't want his friends and gf to be mixed in the same group that i would make it ackward. i don't know what to do?