Maybe I'm playing devil's advocate here, but he said they were friends for 10 years. You said yourself you have male friends (that you used to be intimate with, in fact). Why is this guy so different? Now maybe the woman is looking to cheat with him, so that would be one thing. But are we sure she wants to cheat with him? Maybe she just admitted she used to be attracted to him, maybe she's not saying she wants something now. She is married, after all. Or maybe they're playing with fire. In any case, sounds like she wasted 10 years with him.
You are correct, it could just be that....I will say this. Other than my first husband, who is the father of my children, I do not communicate with ex lovers regularly....maybe a text or two during the year, or every couple of years. Do I consider these men to be friends? Yes, I hope they are doing well in their lives and I might wish them happy birthday, merry christmas or happy fathers day....but I'm not building in depth emotional connection with them. One I've known 35+ years, another 25+.....so I've known them for years - but my in depth friendship and connection is reserved for my husband.
In other words I'm not discussing my current life day to day with old flames....now I do have a number of male friends who were always strictly platonic, those friendships ebb & flow between periods of more or less contact, and my husband has met, or at least spoken with those men, and knows there is no threat to him or us from those guys. I don't go run around out & about with single male friends anymore, I'm very respectful of my husband's position as the man & lover & best friend in my life. All my friends know this.
That is not the situation with OP. This woman is seeking attention from OP that should be reserved for her husband. She is not respecting her husband's position in her life. Its a big difference.