Most Helpful Guy
Well first of all it's not "out of nowhere" since he knows you broke up with your recent ex. He probably thinks he can get back to you. If he contemplated that he's done something bad to you in the past, he would apologize. Did he? No. So should you get back to him? No.
Most Helpful Girl
Your ex didn't pop up out of nowhere. He popped up out of the "I'm no longer getting any on the reg so now I want to get with you" boat.
Basically this person is only interested in you now that they are no longer with their ex. I personally would not entertain this idea. If they truly like you then they wouldn't have done what they did to become your ex in the first place :)
I would just ignore them. Sounds like they aren't really into you, but just into not being single. Not worth it in my opinion.