In that thread I started I a little while back, this was repeated several times:"If you want to cheat, just get divorced." Would a sudden divorce really have been easier for you to get over? I gotta say, 4 years is a really long time to dwell like that and it seems like a sudden break up would have been similarly painful. I know people who have been widowed who've moved on faster. Like I said in that previous thread, this was a specific point I discussed with my wife and her answer was essentially that both would be extremely hurtful.
You think that is as bad as the other situation where you admit you are not as excited about the relationship as you once were and that you might want to discontinue it? That one give the RIGHT of reply to the person. Piece of mind. Still hurtful and still a surprise, but a right of reply and some element of resolution. Perhaps you're taking it literally (the divorce option). Nobody is suggesting that the moment you perceive you wish to fuck someone, you must immediately charge in and demand a divorce. Essentially, you state the truth and let the chips fall as they will.
To answer you comment regarding four years being long. I'm a connection type of person. People who I like don't grow on trees and I've certainly not met anyone whom I would spare a moment for, since that day. I don't need a woman in my life. I don't have to partner up to get through the day. I'll probably die alone and I'd rather do that than spend any time with people who have thoughts like you do. It would be a thoughtcrime to me if a partner thought as you did. That would be it. Maybe that is unreasonable, but that's how I think and that's how I demand they think - otherwise, I'll quite happily spend my time alone - with the only person who has zero percent change of fucking me over - myself. I have plenty to do and my right hand can quickly make me forget about women.
Now, all that is fine, but of course, the horror of it all going wrong and the knowledge that that was probably the last moment for me in my life with someone I thought I could trust and love, often came back to bite me in dreams, thoughts etc. That's just how it is. You can't ignore adversity when there is nothing to distract you thereafter. It's always there.