OP - it reads to me as though counselling might be good for you to deal with your past experiences at some point, but I don't personally think it is necessarily the quick fix you need to help with this particular EA situation right now.
From what you've said, it seems like there are two things: 1) that you are enjoying the attention from this man, and because of your history with him, perhaps it also reminds you of a time when life was simpler/more exciting - to me, that's understandable and normal, but it's not real, because your life has moved on and it's fantasy to think you can go back; 2) that you see an exciting life that he is portraying (might not be entirely true!) and it makes you question whether your own reality is good enough - also totally normal I think!
However, I think it's fair to say that if you delve into this again, the most likely outcome is that you will lose your marriage, either because your DH finds out and won't forgive a second time, or because you decide to leave him in the hope of something more with your friend, or at the very least, because you will have built up the fantasy so far that your own relationship just pales in comparison, and will breakdown or change irretrievably.
I would try to play this scenario out in your head. Take it to its natural conclusion, and imagine how you would feel then. Suddenly the fantasy is gone, but also gone is your reality, one that sounds pretty good to me. If that happened, you would come back to earth with a bump and suddenly realise how much you valued the life you lost. You'd start appreciating your marriage way more, but it would be too late.
If I were you, I would examine your real life, focus on what's good about it instead of comparing it with something that's not even real (even if this man's life is super exciting, it's not real for you) and try to develop appreciation for what you have. Find ways to make your life more like what you want, but as part of the reality that you already have. This other man will be getting a thrill from your attention too. Stop servicing that, and put the energy into your own real life.
Very long-winded, sorry! But I hope makes some sense 