Sunshine, my H walked out on a 30 year marriage, been together over 40 years. We did not D for about 4years but had little communication even though we had 3 grown up kids.
He was married to the OW within a year of the D after swearing he would never remarry.
He didn't tell me or his kids, in fact we have spoken maybe 4 times in 7 years.
His sons graduated, his d married and had a child, he knew nothing of this.
I told him we had a g/child and he begged me to see if his d would speak to him, she did and he visited her, that was nearly 16 months ago and the last we heard.
So hard as it is, it happens believe me. I know.
The only answer is to make a life for yourself and son. He may and probably wont look back.
He is married now like my x. Time to close the door and stop the questioning because there are no answers. I would have found them by now believe me.
We can assume and hypothosise all we like bottom line is,we will never know truly.

It is hard and it takes along time but the sooner you accept it the more life you have ahead of you.
When I first started posting there were lots of us in v similar positions, they no longer post but they are all D and have no contact with x or extremely limited.
Take care of You.