My ex and I? I don't know what to say?

Long story short, my ex boyfriend and I have started talking everyday again. I mean I really do have feelings for him, but at the same time I don't want to get back together with him. I have to drive him around everywhere because he lost his license, he acts really immature, and even though we shouldn't be (he has talked me into having with him a few times since we broke up). The is horrible, I never have a good time and I always feel dirty and guilty afterwards. When I try to tell him this he says, the past is in the past let's move on. But I can't. He was addicted to drugs and put me through hell. He has since gone to rehab and tried to change but I can't say for sure if he has. I just want to be platonic friends with him but I don't know how to say this because he finds a way to make me feel bad, guilty and unworthy when I tell him all of these things. I don't want to hurt him, but if I wait I know it will just hurt him more...please help!?!?!?!?