What do I do when I'm starting to get over my ex and now he's trying to come back?

Simply answer these questions honestly;
1. Do you really want him back? Really?
2. Did he do something to end the relationship?
3. Do you think that the relationship will go anywhere?

If you answer honestly and the answers were 1.Yes 2.No. 3.No.

Then perhaps you should get back together, if the answers are anything else just don't.

You say that you are getting over him, would you rather do that?
You are defined by who you are and not who you are with, maybe you should take a break from men and see if something will happen by itself.