I don’t understand

I find when my bf and I are around his friends he pays all his attention to them and forgets about me. My bf recently had a party and almost the whole time he didn’t speak to me. He left me in his hot tub to go talk to his friends and never came back. Then I asked him to come in the pool with me and he didn’t want to. He barely talked to me the whole time. Which is the same thing he did at the last party he had. Mean while he’s all over me when no ones around. It’s really bothering me. (Btw I’m 17 he’s 19) what do I do?