I think it's simple.. they are selfish. They only really ever cared about themselves. When things started not going their way, it was easy to jump ship and placate themselves.
The thing they have yet to realize, is until they face themselves (the true reason for their unhappiness) they are doomed to repeat the pattern.
That's the other thing that scares me.. there is no way in hell I want to go back to the way things were before. Not sure we (W and I) are up to the challenge to really make it work if that's where we end up.