So sorry you are here Karen. It does sound like your H had rewritten your history to justify his feelings for the ow.
You said the ow is married also but that your H wants to ask her out. Do you know if she has reciprocated or if it is all one sided? Does her H know what is going on? I understand that sometimes you need to let them do what they have to to realise it's not everything they thought it was. I know it's no comfort for you or your girls but there is nothing you can do to change their minds. It's taken me a while to realise this but it's an unfortunate fact.
Read as much as you can on her and post often. If you are angry or sad post it on here so you avoid texting or phoning your H. Cry as much as you want and need to and don't feel guilty. Don't let anyone tell you that you should move on or you should be over it by now. I have had friends tell me that but no one on here will.
Try not to take too much action either. I think you have done all the important stuff to protect you and the girls financially but now don't do anything else to help him have the life that he thinks he wants. Just try get through each day. Take care.
Me - 47 H - 45 D-16 M - 6 years Separated - May 16
Don't leave me behind can't you see me I'm shining... (Years & Years - 'Shine')