FWB keeps trying to convince me to come back with him?

The only way that will happen is if he makes me his girlfriend or just a friend. Neither of which I think he really wants. He really is trying hard to convince me. I keep telling him no. I really do like him, which he tride to say that I didn't. He said he's treated me right. He has been really sweet for an FWB, but I've told him I want more. I told him it wasn't healthy for me and that I need to be in a relationship. He kinda skirts around that little fact. I don't know what to do. I'm not going to go back to him but hes not giving up. I don't want to block his number. I just want to convince him the next time I talk to him. What should I say so he knows that I still care about him but that I just can't be fwb?