I am so sorry this happened to you. Relationships are scary. I feel awful for you and your children, but it seems that your husband or ex husband is an immature cheater. I would say he has had this girlfriend for some time and is not using that as a reason to leave you. They say the grass isn't always greener on the other side, and I hope he realizes this once he sees what he lost. I do wish you the best, and you and your daughters do deserve better.