Thanks again, everyone. Especially the ladies as your views are particularly interesting.
I think it worth pointing out again that I really don't see this going anywhere; in fact, I would be shocked if it were ever to turn into an all-out affair or a let's-divorce-our-spouses-and-move-in-together situation.
My initial post was more one of frustration and venting about these thoughts that I am constantly fighting to keep under control. I had a weak moment and reached out to anyone who had anything useful to say; it's not like I can discuss this with anyone who is part of my day to day life, after all. Believe me, I'm not a total idiot.
OTOH...
I want to add that, as stated earlier, I have been married for more than 30 years and, in that time, I have worked with hundreds of women and known hundreds more outside the workplace. None of them has ever moved me the way this one has. And, no, I have never cheated on my wife. Not once.
But, I will also add that my wife and I have been just floating along with the current for years now and yes, I have tried to change that. Anyone who has been married for a long time can tell you, people grow in different directions and it can be difficult to maintain the "magic" that makes a marriage work. It's been a long time since I felt the magic and, sure, that is probably part of the problem here. And, yeah, as I get older, I am troubled by the things I haven't done, things I have missed out on, and the things that I will never do if I don't "take the bull by the horns" as we used to say.