You might try looking at it like this: name-calling is abuse. Abuse is bad for our health-regardless of what form the abuse takes. The secret to why this happens to you might be in what you wrote: "I try to be understanding..." Maybe you should stop being so understanding. I have noticed people who are caught in abusive relationships often explain or attempt to 'understand' the bad behavior of their partner. But people need and are entitled to boundaries that keep them safe and emotionally ok.

Have you had counseling? This would be a good topic to discuss with a counselor. Personally, name-calling would be a deal-breaker for me. As to why he is doing it now--wouldn't matter. The fact that he has that sort of behavior inside him that he can pull out and use on me? That would be the end of the relationship for me. I hope this gives you some perspective.