If one of your friends came to you and told you that his wife was having an affair, what would you tell him? You'd probably tell him that he shouldn't put up with that behavior from his wife and that he should toss her out and move on. The problem with many of us nice guys is that we have the opposite reaction; we beg and plead and try to do everything possible that we believe will save the marriage. Unfortunately, what saves the marriage is exactly opposite of that inclination to be the perfect husband and showing all of our love and affection. You have to show the spouse that you're just fine without them; show the spouse you're ready to move on (and you need to sincerely believe that).
So, I think "being a d-ck" is bit of a misnomer. It's more along the lines of showing via actions that you're not going to put up with the cheating sh*t and you're moving on to greener pastures without having a third party in your marriage.
