DG..I am sorry you are going through this. You know we all love you and want the best for you. I want you to make your decision with open eyes, heart, and mind. I though my ex and I had a chance to work everything out. The things she did tell me when we did communicate gave me hope. What I didn't know was that she was already in a relationship with someone else and was just doing what she had to do to keep me hanging. She still got whatever she asked for from me. Don't believe ANYTHING your H tells you. If you think your H is having a PA with this woman, then he probably is. Don't try to convince yourself over the next week or two that he isn't.
Those of us that DB get usually get hurt (at least) twice in the process. The first is when we get the initial "I want a divorce". The second is when we realize that we couldn't save our marriage and it is completely over. The second time is a lot easier to deal with as we have all learned skills through this process to help ourselves. It still hurts though.
I hope I don't sound callous. I just want to give you a not so rosey view of all of this. Everything you have wrote to us about your H tells me that he is extremely selfish and doesn't care about how you feel. He wants everything he can get and will take it all if you let him. You need to take care of you (and your children). Maybe you taking the next step will make him realize what he has done. Maybe it's too late for that. Just take care of you DG.