To be honest, without being brutal about it...
Not enough time has passed for you to truly have changed any of your self-sabotaging ways. Frankly he'd be stupid to take you back, regardless of how much he cares about you. If you want him back, you need to apologize, take some time to fix your own problems, and then try and regain his trust. If that even works, and you'll have to be willing to eat a lot of crow about your behavior for a long time.
Everyone likes to be the exception to the rule, but frankly most people really just aren't, and even fewer are willing to truly look introspectively and understand why the things that are broken about them are, and are willing to undergo the emotional pain of fixing it.
You're expressing remorse, but haven't said anything about what you've done to truly go about changing yourself, and change takes time. Not weeks, not days. It takes months, years of work to get better.
I know, because my wife did something similar to me before we were married. It was extremely painful for me, and when I was in proximity to her it was easy to let my guard down and resort to feeling comfortable. But, that comfort wears off eventually and the fears, the insecurities, and the mistrust sets in. That's when it gets really hard to deal with.
Frankly, he's willing to sleep with any woman that's willing to sleep with him, and well, you were the port in the storm that time.
It's probably easier if you just let him go instead of screwing yourself further emotionally without taking the time to address your personal issues that led you to screw around with an ex while you were in a committed relationship. Because, frankly once you cheat, the next time is easier. And, you always wonder from that point forward if you're capable of being loyal and monogamous.
"Well, then," the Cat went on, "you see a dog growls when it's angry, and wags its tail when it's pleased. Now I growl when I'm pleased, and wag my tail when I'm angry. Therefore I'm mad."