Congratulations on your new baby girl! And that's just the way you should look at it. Having a baby doesn't keep a marriage together, and the sex of the baby doesn't either. Now you will have 3 beautiful little girls and he will have . . . . .what?
If he turns his back on his family, his loss. You listen to the others here and be strong for your girls and for yourself. Be the grown up in this picture. As much as you grieve, he is doing this to himself and you can't fix him. So at some point, you have to let it go.
