Talk to him about it first. It's a very unhealthy mindset and he could do with a dose of reality.
If he's unwilling to admit he's making a big deal out of nothing then, yes, it would be wise to leave him. Problems like that don't go away unless the paranoid partner is willing to admit they're being irrational and work on it.
I've a male best friend. Going out with him for dinner & wine Monday night. My partner isn't threatened by him - he knows it's platonic.