found out my RECENT ex boyfriend was sleeping with others during the relationship?

[Luce):)]

hey so , i was with my boyfriend 3 years, he was violent, abusive, controlling, anyway, i stayed with him because i thought unlike so many other guys he was faithful, i finally got rid as i was sick of his use of drink and drugs and just the whole abusive persona, never understand why guys like these have girls for SO long, but hey :\ guess i helped him there.

around a year ago, we broke up for a while and i thought we was over for good, i slept with another guy, my ex boyfriend came grovelling back, with a note that i thought was quite sweet, i felt really bad about sleeping with this other guy, so i told him, he forgave me, and we got back together, and everyday since he made me feel like a worthless slag because of it, i know what i did was pretty naive and slaggy, but it was a mistake and i never went near a guy whilst we was together.

i found out last night, he'd been sleeping with other people, from the start to finish of our relationship, which i was completely oblivious to :\ and all those times he accused me of doing this and that, do you think this was because he was cheating? what can i do to get over this idiot?