friends with benefits could turn into...something more serious?

A slightly different take, I guess.

Sometime soonish, tell the man what's on your mind. If he goes for it, hooray. If he doesn't, well, you now have all the reason in the world for a clean break, which I think is a good thing.

If you guys are really that good friends, things will be awkward for a couple of days, even a month or two, but things will go back to normal eventually. In that time, you'd probably get over it, find someone new and be ready to be a proper friend to him. If not, well, it's a shame, but you're better off not torturing yourself with long-shot wishes every time you're with him. You'd best be getting a clean break and moving on at least now knowing.

Jam it back in, in the dark.