Hi,
I cant believe those things still happen when you are in your fifties! I cant wait to get out of my 20ies and I hope I will settle down and never have to worry again ... crazy world.
Anyways, I believe you are so attracted to your "friend" because he is a challenge for you. Your marriage has become boring over the years. This other guy represents an adventure and he makes you think about things you are not usually thinking about. He is mysteric and unreachable - it is like a goal for you to get him and the longer he lets you hang the more obsessed you will become with him.
This is what I would do in your situation: Be strong and wait for HIM to contact you next time. Make sure you keep the whole thing as a FRIENDSHIP!! You dont want to loose your husband - he doesnt deserve that. Try to talk to your husband about your attraction. You have not cheated yet, you can be honest with your husband and try to find out what is missing. Honesty will help the most in this situation. If your husband is understanding you both can work on a solution to pep-up your marriage and maybe do more things together, challenge each other and maybe start a sport together. You seem to be the competitive kind, like me, and I found doing sports togerther hepls a big deal.
Please dont get together with your "friend" and be strong! Let him get back to you and cool the relationship down. Maybe even tell him what you feel and break up the contact for a while.
That's what I would do - Good luck to you! Keep us posted!