Girls help me please?

my ex boyfriend is a hyper-ual but takes medication to control his urges. we were not together but "together" for 5 months and in may he told me he loved me and i already knew i loved him so we made it official. we were together for a great month but in the middle of june he was in italy and called me. he had gone to a party in venice with his friend antonio, didn't take his medication and did some girl, who's name is gianna. well he thinks that's her name. i told him we were done, and it killed me. when he got back to the states, all he did was text me and call me and facebook me and in every message he always said 'i love you' at least twice. its been two months since we broke up but every time i see him online or he texts me, i always feel like i did whenever i found out. i had told him previously if he ever cheated we were done, because in april he had this girlfriend he didn't care about and only went out with her because one of our rules was we couldn't date, along with not falling for each other. he cheated on her with me. they didn't do anything together like we had, though. but i really miss him a lot, and he is really trying to get me back, and my resolve is falling. i still love him. but i don't want to have to deal with this again, which i have a feeling will happen. he's in college now and i'm still in high school. does anyone know what i should do?