Can't get rid of him

this man has been accusing me of his co-worker saying where having sex and he's coming over it's ridiculous I've told him time in time again I never even talked to this guy outside of being with him I don't know if he really believe it or he just does it cause he's doing something or it's a mental issue but by the stuff he told me about his past relationships seems like he was thinking the same thing was going on or something similar he gets abusive about it I really fed up with it