I am SO sorry to read what your husband has done to you!
I wish that I could understand his motivation behind his strange behavior, it makes NO sense to me whatsoever. Regardless of him wanting to now split up, he is still legally responsible for your and your baby's care. I wouldn't let him walk out on those responsibilities.
Maybe your hub has been overcome by desires for different women, to add to his tally.

Whatever he's thinking, I can only imagine how painful these past few weeks have been for you. You have to take care of yourself and your baby though. Try to think about positive things, to get yourself through these last few weeks of pregnancy. Focus on name choices, decor, clothes, etc.
I do wish you the very best. I hope that things begin to improve soon emotionally. You deserve so much better than this shoddy treatment by your husband. Don't ever doubt that.