I am sorry mammablueeyes, you made a bad choice, and IMO, if you want to remain with your H, you never ever tell him, live with your guilt and do everything in your power to cut contact with this man. That is a measure of how much you love your H.
Speak to the man and make that clear and hope he has the humanity to respect your decision. His 'love' for you may be an emotional crutch as you supported him following his relationship break-up. And given the rarity of true platonic friendships, that was possibly a mistake in itself.
My marriage has broken down slowly and painfully over the last two or three years and somewhere along the line, I felt a chemistry with somebody, most of the time the guilt of that alone was enough to make me throw myself into trying to make my marriage work. I probably stayed with H longer than I would as a result of that guilt, and subjected my DC's to suffering seeing their father develop a complicated drinking problem.
Even up till recently I would have moved to give my marriage a chance, despite my feelings for someone else, and if H could have kicked drinking.
But now I am having my heart broken in every direction. H moved out today, i feel vulnerable to my feelings, because I am to all intents and purposes on my own.
'He' is married and yet the times when it has taken every fibre of my resolve not to reach out to him are enough to make me feel ashamed.
Please mbb, don't go down that road. Sort out your sexual compatibility with H. With time and effort, it can be done. Good people don't deserve to be hurt....have a life assessment, sort your priorities, forgive yourself this mistake, but resolve never, ever to do it again.