kai, A lot of them do marry the OP. They are trying to prove a point in most cases, i.e., that it was us that created the breakdown in the marriage. Or, they do it when they are most vulnerable and don't know how to get out of it. Whatever the reason, many of them regret the new marriages, but won't always admit it.
As for him feeling the way you have felt....time is on your side. Give the euphoria time to wear off. He may be flying high right now, but in a few months or even a year or so, the brass will tarnish and he'll be down in the mouth once again. Karma has a way of coming back to bite them.
The most important thing you can do is take care of yourself. Focus on what you need to do to get through each day and go from there. The man upstairs will take care of your h.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.