He chatted me on facebook...now what?

No as a guy i would say he wouldn`t care at all that you didnt respond and if he is after you so much he wouldnt care that you didnt respond one time, and please put him out of his misery so he can move on, i never think its cool if a girl i like just wants to be friends when i clearly express my feelings to her, put it out in the open, say you can stay friends, you just dont want anything to do with him relationship wise. Also if he likes you that much, you might want to try and give him another chance, it seems like your always on his mind, so id say give him another chance, thats just my opinion on this