J.L.
He is able to cut off his feelings and reject you because of 1. proximity, 2. exciting new relationship, 3. no responsibility. Research proves that there is a marked decrease in marital satisfaction after having kids. Wife's focus tends to more on the kids (out of necessity). Husbands OFTEN feel neglected. What he has now is a wife taking care of his children while he gets to have a girlfriend and play: best of both worlds.
Its so much easier to cut off feelings when you choose an entirely different path. You are still, essentially on the same path: mother, working, etc. The dream of the future that you created doesn't match up anymore and its so difficult to reconcile to this reality.
I'll tell you this: you will be on this roller coaster for a little while and will handle it much better if you draw in a lot of support for you and your children AND take the time to allow the feels to come, really feel them. That's the yucky part, but don't shy away from mourning the loss, missing him, loving him, your own regret, anger at him or yourself, pride that you are putting one foot in front of the other... Don't cut off your own emotions! Years from now, if he hasn't dealt with what he created, he will be in a terrible fix. Whereas, by dealing and feeling what you've been dealt, you will come out stronger. And you will come through it though it may not look like it today.
My heart goes out to you!!
Jen