I am so sorry. Just concentrate on your kids and get support from friends. Just know that it gets easier once you have made the decision which way you are going. You may feel powerless, but the ball is in your hands too. If he walks away from his family, it is up to you if he comes back or not.
V960 made a comment that something you have or have not done must have made him leave. That’s not always the case. Sometimes it is something lacking in the other person. In rough or tedious spots in a marriage a new romance makes them feel like superman, only they are not. They are people who break marriage contracts and leave their kids.
It does get easier and sometimes as a result gets even better in the long run.