There are implications in some states about this issue. You need to consult an attorney and NOT the one you are sharing with your ex. He now has every legal right to stop divorce proceedings and delay your final divorce. He can say there is a pattern because you've hooked up after filing a couple times.

It's hard to transition to a new life after marriage and you have a lot going on. You deserve better than you are allowing yourself to find with some of your choices. You may need to find a way to a therapist to understand why you keep returning to someone who repeatedly hurt you. Understanding why (trauma bond) is not enough. How you are going to heal from it should be your focus.

I'm split on telling your friend Jay about it. I don't know if you agreed to be exclusive while taking things slowly. If you said you would and now you didn't, he deserves the truth. If you don't have any such agreement, I think you should keep it to yourself for now.