Well Starsky, I gained information about why she was attracted to him as well.
To begin with, this was her ex-boyfriend from high school, someone she has known a long time, and she has confirmed that he was the only one this could have happened with (I am not foolish enough to take that as salt, but I believe their history together made this possible.) Where I am abrasive and a fighter, this guy was calm and understanding. (basically, he's a pansy) He is also married with 2 kids of his own and living many states away. This was almost entirely an emotional affair. Lots of talk of love and what not and very little action. Though they did meet and 'kiss' when they went back home together (and I am pretty sure this was all that happened, but I will never really know.)
I won't spend too much time conjecturing on why that was, but I feel my W did not get the emotional connection she needed from me and he filled that hole for her (there's a pun here as well but I won't mention it. Like I said, I don't think that happened.)
See my W is a fighter too and doesn't know how to back down anymore than I do, but this guy backed down as a matter of his nature (maybe he was abused as a child), but I think his passive voice is what led him to his own difficulties in his own marriage. But my wife didn't get resistance from him and she felt better with that (plus I had been depressed and really negative for a while; i.e. really arguementative). Again, I am psychoanalyzing here, due to many long months of reading about relationships and the roots of infidelity.
Physically, I rock my W's world in a way this guy never could. (maybe this is my ego speaking) But I know where my deficienies lie as well; and that is in emotional support to her (and in her to me as well). If we could reach that peak I think that things would be so much better between us, and that is what is missing and needs to be fixed.
Can this guy take her back? Maybe, but he will have to leave his wife and kids first (and grow some balls) which I don't believe he will do. My W needs to understand that there is only one man willing to stand up and fight for her (and it is not the passive calm pansy). And I need to show her that I will be supportive of her feelings and only fight for her and not with her; except where it really counts.
Was what she did sick, yes; was it betrayal, yes; did I have a break down in which my world was flipped upside down, yes. I nearly lost everything I really cared about and that was brutal. But I am back together now and working to save my marriage, because even though there are a lot of sweet things out there, she's the one I dedicated myself to and I plan to live up to that vow.

Forgive the extended soliloquy.