I am glad that you found a lawyer that is efficient, but she is blessed with a very organized and terrific client. Make sure that your kids are well provided in the future, include a monthly or yearly deposit in a college fund under their names by him or both of you, just make sure your are the owner of the account. Also, add that child support/alimony if any should be back up by a life insurance under his name that he has to pay yearly and he should provide you with a proof of it. All those "details" were provided to me by a very dear friend who went through "a lot" during her divorce, her husband had found his supposed soulmate... but she managed to make sure that "his wife of 25 years" got served first...
Wow your first D-day was October 4th 2015, on October 5th of 2015 it's when I discovered that my WH was back with OW 1 after first DB on June 2015. I remember how distressed and sick to my stomach when I got the news.
I don't think that telling whatever to that nurse is a good idea since you decided to file anyway. It might get him very angry at you and lower your chances to get a good deal from him during that process, but you might use it as leverage over him if needed later on if he still in touch with her, to get more of whatever you might want from him.
Use what you have on him to gain advantages (kids' custody, alimony, retirement, house, college funds...) since he cares about his reputation (mine is like that too). Look at the long term satisfaction not the short one.
Act/think instead of reacting, tough but you show us that you are very smart and determined. Don't make any decision without taking time to think about the eventual consequences. Have also plans A, B, C, and D and more if needed, be ready for whatever might come your way. Think of it as a chess game.
I had a very good day today, I am blessed with wonderful students, they are making me lose my mind pretty much every day (teenage boys) but they have been a blessing through those years of ordeal, their enthusiasm always got the worst of my sadness in just a few minutes.
Allow yourself to grieve/mourn your relationship and what your life could have been without his bad decisions, it's very important, and then turn your mind/energy to the future and start making plans/changes that will transform your life for the better. You will be amazed to rediscover activities that you used to like or do but you stopped because of him.
Me 52+ WH 57+ Married 20 + Piecing since 2016 (ready to give up...)
