bf losing interest in me

i have been with him for almost 5 months now but recently as hes started a new college he has met new friends (which doesnt bother me) but has got extremely close with another girl named chloe. he brings her up in every conversation, sends me pictures of them two together alone, tells me how nice she is and even cancels on our plans to meet her. he even went to her birthday party, which was full of girls and goes to her house and multiple house partys with her. i never get invited to these. i cant tell him to not go or to not be friends with her because i dont want to be controlling but i dont know what to do about this as it is making mine and his relationship a lot weaker.