I'll tell you what!
Isn't he lucky you haven't knocked him upside his head and laughed him all the way down the road.
Yes, he has a charming, sweet and loving side. So what? He doesn't value it enough to develop it into the major drive of his personality. Further, he is like a teenage boy who has fits like a toddler.
For an adult, that's too self-centered to bother trying to develop a relationship with. He's unpredictable and undependable. Do we want mates or big children? (not to say we shouldn't honor the "child within", but that's another story)
If I hadn't been through this exact same thing, I wouldn't feel so strongly about this. My guy also became very sad, before getting 'round to calling me names AGAIN.
Best wishes.
(ps/I see you didn't cheat on him, merely began a friendship because he pushed you toward it, then saw it grow. By the way, congratulations, Mr. New must be a Nice Guy.