I've been married and divorced three times. Two ended because I had affairs and the other ended because she had an affair. In my opinion, an affair starts out as a bit of excitement a bit of fun. No, I don't think anyone thinks as far ahead as damaging a marriage. It's what the affair becomes that is the important factor. Short term and, some long term affairs, will, never affect the marriage because your partner is none the wiser. I chose to tell, on both occasions, quite early on in the affair, because i was sure that i wanted to be with the other woman. I married both the women and after cheating on my last wife, do not intend ever marrying again. I am not proud of those affairs, I felt sick to my guts about what I did to my wives and still do. When it was reversed, and my 2nd wife did the same to me, it was easier to handle, I only had my own sorrow and anger to deal with. If I had my time again, I would still be with my first wife , and watch my two children grow into the great people they are today.