I have to say that not all spouses who leave and have ow have a reason to.
I can tell you that my h has told people that there was not a problem in our marriage, he does not know why he went out and had an affair, that he was happy in our marriage. We always talked, never argued, that sort of thing.
I think they try and convince themselves that the grass is greener and the op is right there filling their mushy brains with false hope. Then they get caught in a web of deceit amongst other things and they feel they have no way out.
The Bomb: 08/05 H moves out: 06/2006 H moves back: 01/07 & Out again: 01/07 H moves back: 03/08 & Out again: 04/08 H moves back: 05/09 & Out again: 07/09 Divorced 08-12 Kids: 22, 20, 19