Having been in this type of situation before as the guy, and knowing I wanted the friend badly enough for a relationship or sex and she didn't want that, the best thing to do in a social sense is to just fade out. It might be easier to sustain friendship later on if done respectfully as well. And yes, if me and that friend aren't on the same page, we usually stop communicating. That just seems more respectful as well as saying something like "Wish you the best moving forward."
Be warned though... this guy's frustration that you don't want more may come out. If your friendship with him didn't end before that point, the frustration coming out probably will.
_________________
Your Aspie score: 130 of 200
Your neurotypical (non-autistic) score: 88 of 200
You are very likely an Aspie