Is there a way i can fight these feelings?

Im 15 and im having mixed emotions. I dont think thats good for a person my age. Thing is, i have a boyfriend and we've been together 8 months. He's away on holiday and has been gone away for 3 weeks. Theres this other dude who i used to go out with and when we went out we had a series of going n breaking up and so on , like a rollercoaster. This was like when i was 11 and 12. Lmaoo. We broke up when i was 12 and igot over it quickly. But then, i started to get those feelings back but this time it was different coz he didnt feel the same. I spent like 2 1/2 years trying to get him back and as i grew i realised i really did love him. (he's 16 btw) Not just any crush buh i had those true feelings for him. He has this girlfriend now, who he cheats on with my friend, but he doesnt know i know, and she cheats on him too (his girlfriend) and she doesnt know i know. The other day, me and my friend were talking about him and i started tp get those feelings back. I hate him with pion (well i try, coz if i only like him, i know for a fact ill end up gettin hurt). So now, im forcing myself to hate him, which is working, but those feelings are comin back. And im missing my boyfriend too. I really love my boyfriend with all my heart and i dont wanna be selfish and hurt him. Btw its his bestfriend as well. I accidentally told the other dude i hate him on facebook. I feel bad. But i feel pathetic and small too beacause of the was he spoke to me. When used to be friends wih him, id try and talk to him but he was really hard to communicate with. I just dont know what to do about these crappy feelings. One minute im all confident and the next im reeeally sad.