I am so sorry to hear that things have become so bad. It seems that he has already checked out the marriage and as you say is lining up wife number two. She is as bad telling a married man she loves him. Your husband may wish to divorce and start again but he is forgetting that divorce for anything other than adultery does not leave him free to remarry. Him and his floosie have no right to a relationship unless immorality occurs under his rules. He is setting a bad example for his daughters. I am truly sorry for you but he seems very immature and you do deserve better. It is natural to mourn a relationship especially one where you have children together. What is important is to think about what is best for them and for you.
You have received a lot of good advice only you can decide if you want to give your marrige another shot. If you think it is over then take control of the situation and make sure it is as stable as possible for the children. They are young enough now to make a transition and adjust.