I think if I were in your position I would say my good byes. Why waste time with someone that you seem pretty clear is not going to be someone you want to be with for the long haul. If the sex was great then yay, tell them that and add that you just aren't into it any more. If you like to sit and cuddle and watch movies now and he does too then yay, but I think I would be honest and say that you don't consider him a bf any more but a friend. Maybe he will be cool with that, maybe not, but at least you can do him the honour of deciding for him self. I know I would feel very disrespected if I knew someone was hanging out with me and fucking me out of a sense of obligation. No thanks. I'd rather they be honest and then we can go from there.
Next time I think I would remind myself to let any new sex partners know that I am fickle when it comes to sex sometimes and that it might be better to wait to commit to the bf/gf thing until the sexual NRE wears off. I think I would assume each time that its just exciting to fuck someone new and be honest about that with them. That way they are dually warned and if it goes somewhere more then great and if it doesn't then at least you have warned them. Maybe not warned them so much as been honest about the way things work for you.
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