I'm pretty sure that a lot of people will jump on the "he can't hold a job" and you've "supported him for years" situation. That's not always a deal-breaker, though. What are the reasons he can't hold a job, btw?

That he lies, has cheated, and leaves you is what bothers me. That he says he's never loved anyone, never felt empathy...something is terribly imbalanced...I'm going to guess that he was raised in an abusive, very troubled home?

From what you've posted, your partner is not entirely your partner and honestly, it sounds like he's using you as his meal ticket. From where does he obtain money when he leaves for weeks at a time?

If I were in your shoes, I would feel like I was losing my mind, too.