Above all else? Be Kind to Yourself. This is going to hurt, because it's a really shitty thing he did. It's unacceptable, unreasonable and utterly, utterly cruel.
MN is never fed up of hearing from people that need help, there is always someone here to give you a hug, listen, and hold your hand if you need it. Boot you up the behind too if that is required [cgrin]
I'm heartened to hear his parents are coming to see you though, that's good news I think, in that they are caring, normal, decent people. It will be hard, but it has to be, let it out if you need to, they ought to see what their son has done to the mother of their grand-children.
Anger is a phase you will go through, a split like this, the end of a relationship needs to be mourned. The loss of the past, the loss of the present and the future. In time it'll ease, keep talking to those that can help/listen, lean on MN as much as you need to, and contact RL counsellors if you think they can help.
Remember you didn't let your family down, you are the strong one, you can 'hack it', he is the wimp that can't. In time you will regain your strength, you will recover. He will always be the shit that walked out on his DC.
Hugs to you my dear, and to all those that are suffering similar.