Relationships issues

I have been on and off with this guy for almost 2 years. We both have done wrong in the relationship but worked through it. Now he is accusing me of sleeping with this guy I was friends with which I never did. He constantly brings it up everyday as if I did do something but I haven’t done shit wrong. When he accuses me because it’s been everyday for a week now I get pissed because I’m sick of hearing about something I didn’t do. What do I do? Is he being insecure? Is he cheating because he’s making accusations? I don’t understand and I need help.