Tostada, I worry that the anger might be running your life too much right now. It might be worthwhile for you to go see a counselor so as to get some coping strategies on how to get over the anger.
Dont worry about the over/under of their relationship. It may work out, and if it does, you need to not be waiting around indefinitely for it to fail. My mother is still with the man she had an affair with that broke apart my parents marriage and it is over 30 years. My father did not dwell on it too much although he did refer to OM around my brother and I as "Fat Boy".
Maybe she will be happier and it may not be such a bad thing for the kids to have a happy mother. Your concern is for when they are with you that they have a happy go lucky father.
Please try to work out some of your issues regarding your anger. Getting rid of the hostility about the terrible breakup of your family will be best in the long run.
