The part where he cheated on you bothers me less than the part where you said that he admitted to treating you badly for awhile now..

That makes me wonder if he CAN change. Also if he's only cheated once. I mean, if he always treated you great and made one mistake, and then did all that to get you back, it would most likely warrant a second chance to me.

Of he's been treating you like crap for awhile, and things aren't the way they should be and haven't been, that's a red flag. I would have suspected the cheating the moment he "changed" and started treating me bad.