my boyfriend's (girl) friend

I know I must be over reacting. And before anything I know he would never cheat on me. but he hangs out with her at school everyday, they have many of the same classes together and they have much more in common than him and I do...i feel very insecure and whenever he talks about her I start to get sick and shaky. he always post him hanging out with her on Snapchat and I can't help but to check it. I get so sad and angry when I see them together. is there some way he can lock up the sc app so I can't get into anymore? I need some advice