Well, as a rule relationships are touch and go, at best. To the testament of many failed relationships, I've run into a number of people, who really do not understand what a relationship requires to be successful and long lasting. Now- I understand your situation, because I had the same issue with every single girl I've dated. The problem isn't deflection of blame, the problem is a lack of morality. He simply has provided you with the most basic character-check, if there was one, about his true being.
He is just as lost as you are. He cheats on you, not because of you, but because he cannot control his sexual urges. He breaks morality, damaging his character, every time he sleeps with someone else. His actions are morally wrong. IF that doesn't tell you who he is? Then love him for what he is and be done with the complaining. If you are hurt by his action, then you already know it's wrong, yet you LET him put you down, for something he has a problem with. More sex sounds like a solution? But, I am really nobody to say that. However, it's obvious there is something wrong that needs correcting. Unless, you like feeling guilty for some odd reason, but I'll leave you with that thought. :)