what the fuck is wrong with him

Okay i need help. My boyfriend and i have been dating for 4 years now. There was a time when we broke up because he moved to a different city and it was just complicated. I tried to move on and started talking to a new guy. Well it didnt work out because i was still in love with him. so we made it work out. well theres this old friend that started texting me. As FRIENDS!! and my bf started telling me that i should be careful not flirt with him telling me that i was going to cheat and shit like what the fuck he's just a friend. What do i do??? he's acting like if im going to cheat whenever i have guys friend..