You should buy the book "The Script." Your husband literally did word-for-word what all men do when they have affairs and leave their wives. He's not special. He didn't meet someone new and special who will change his life. He and that woman are nothing more than textbook stereotypes that will fade out in 18 months like over washed denim jeans.
Also, now is the time to focus on bettering yourself too. Work out, learn dancing, find yourself again -- find who you were before you become a mother and a wife.
You know my father had done the same to my mother and abandoned the family. And my mother told me that he said he no longer loved her, he never loved her, he made a mistake marrying her, and they needed to divorce ASAP. He left her for his secretary who was 15 years his junior. They didn't last more than 3 years. And, she left him for another man.
12 years after the fact, my father repeatedly apologized and stated leaving our mother was the biggest mistake of his life. He regretted everything and felt he was being punished for his actions. His life was in a terrible place at the time.
And, he told us this, "Every single relationship has fireworks at the beginning. You feel like you are in love with the person and nobody else on this planet will compare and it'll last forever. But, know this. it's Nothing but boredom and infatuation and it will always, always fade no matter who the person is. When you find the one you want to be with, don't let go. Even if you're feeling fireworks somewhere else. Do what you can to strike it back up from home."
And that's what your husband should have done. I'm sorry.