Pud is right. Write it here first. Go back to the basics. You want to be the one he doesn't want to lose. And, you are! If that wasn't so, he would be living with OW full time.
I know we sometimes feel like "home base," but we need to find a way to use that to our advantage. They can't let go of the rope and there is a reason for that ... the grass is not greener. There is a connection that they don't want to break. They just have to figure that out for themselves. But, we can help them along by being that amazing, incredible woman who loves them enough to let them do exactly that.
I know you ache for your S, but you will have to do the work of two for the time being. Fill his (son's) life with as much happiness as you can.
Please, dig down inside and find the patience. I know it's tough ... I have a hard time with that myself .. but dig. It's there!
Put a smile on your face and be the person that you know are ... resilient, strong and capable of weathering any storm.
Hang in there. You know you can.
Me: 59 and holding H: :53 Me: 1 S, 1 D, both grown M: 19 T: 23 BD: 9-23-2013
