His happy ever after just doesn't matter in the long term, not to you anyway. Anytime you start to get caught up in that thinking and dwelling in it, that should be the cue its time to challenge the thought. Tell yourself its not productive and then shift focus onto yourself.
Its not effective to try and not think about it either, that's still putting the focus in the wrong place, on him. If someone tells you "don't think about a giant pink elephant", that's what you will do. You want to fill your time and life with other activities (GAL) that you enjoy so it leaves less room for that type of thinking to consume you.
If you're spending your time building up and improving your own life, how his turns out will be of no importance.
Accept what is, let go of what was, and have faith in what will be
