Mrs D...I hope this doesn't sound harsh, but I am going to be blunt with you. Stop tryin to contact exH, don't make your son contact him knowing you will talk with exH, stay off of facebook (I thought you deleted it), stop asking about your exH or his gf to friends.
What you need to be doing right now is concentrating on YOU. You need to fix yourself. You won't do yourself, your exH, or your son any good if you don't concentrate on you. Your old marriage is over. Nothing you can do about that. What you can do is fix yourself and see if your exH can fall in love with the new you. But you aren't there yet. You can't run until you can walk.
I don't know if you will end up together with your exH..But I do know that if you listen to the people on this board, you will end up a better person, happy, and loving life.