boyfriend and SO many girlfriends

let me start out by saying that I am in no way one of those controlling girlfriends that allow no woman to have friendship with my man. I am friends with a couple of his female friends but there are a few others that really do not make me happy. me and my boyfriend are in a long distance relationship, we go to college about 4 hours away from each other, which makes this harder for the both of us. I have bought up MULTIPLE times how much him hanging out with certain girls makes me uncomfortable and upset and every time it's "she's just a friend and I don't understand why you don't like her." He also still stays in touch with a couple girls he met as "friends" on tinder that he previously hooked up with. Im tired of being told that I am overreacting and that my feelings are invalid, so what should I do? Say something? Grow up and just be quiet? I'm not really sure