I don't agree with anyone hitting anyone, for any reason. Women cry abuse if a man hits them, and it's no different if a woman does it to a man....I don't buy the 'weaker sex' excuse either. Physical violence is an extremely poor outlet for anger, and infinitely more disrespectful than the behaviours he displayed that brought on this slap. Your relationship is unhealthy on the whole; and if he's so fed up with you he has to pack up and leave every time you fight, I'm guessing you're 50% part of the problem. No offense intended, it's just how I see it.
No man should put up with being hit.
Live as if you were to die tomorrow. Learn as if you were to live forever. - Mohandas Gandhi