On Flirting

I am married and my husband and I have a strong friendship but no intimacy and we still enjoy each other’s companion and so choose to stay together.

12 years ago, when I was still single, I had a one night stand with an executive from the company I used to work at. It was exciting, forbidden and sweet, but he was married (still is) and that was that.
Yet ever since that night, he kept in touch with me all the years, sending me Happy Birthday greetings, and every few months checking in on me and how I am doing.
When I told him 10 years ago that I am getting married, he said he ‘felt sick to his stomach…’

Fast-forward to a few weeks ago, he reached out and said he wants to leave his wife and that he was in love with me all those years.
I don’t feel the same way towards him and I don’t even know if I would feel any attraction to him had I seen him after so many years, but there is a part of me that keeps allowing him and myself to flirt.
So we don’t see each other, we spoke on the phone a few times, we text and email to each other and I run two Models.

Model #1:
C = Sexting with man
T = This is wrong because it’s not how I want to be in the world and we have no future together.
F = Shame/Guilt
A = Want to cut the communication, contemplate how to tell him, consider avoiding him completely and blocking him.
R = Staying faithful and making sure we have no future together.

Model #2:
C = Sexting with man
T = I know it means being unfaithful but if I cut communication with him I won’t have this delicious attention and I won’t know if we could have a chance at something.
F = Fear of missing out.
A = Keep sexting him occasionally, trying to coach myself.
R = I am being unfaithful to my husband and to myself, I get only crumbs of attention from a man who belongs to another woman.

I think what my brain fears is making a decision like cutting all communication with this man because it fears that there could be something here potentially in the future if I will choose to divorce one day and if I will let this man go I will never know if we could have been a good fit someday.
Yet, flirting and sneaking around now, in hope to grab onto a call here or a message there doesn’t really feel satisfying. It feels like stealing something that isn’t mine.

The way my brain interprets the two Models is that I lose either way, that either choice feels unpleasant and produces negative results.
Would love your help on that.