Hi, I am sorry that you are having such a very rough patch. It must feel like h*ll right now.
But you have been given some good advice. Your son will come around. Please, for your sake and his do not be bitter. Your son isn't in a position to make good choices right now. I have no idea what things are like at his father's house, but if you let him stay there, and relish the freedom, you will find that this relationshp will come right. If you are bitter, and let your feelings of rejection show it will take longer for your son to be comfortable around you
Children need BOTH parents, however unsatisfactory. The fact that your h is now prepared to have him to live with him is a huge plus, whether you see it that way or not. Your son no longer feels rejected by his father, which likely contributed to his behaviour issues. Your husband can no longer blame everything about his son's behaviour on you, and his relationship with OW will encounter a little reality.
Focus on your daughters, especially the younger one. Your elder daughter will be leaving home for university soon, and so this could be a very special time.
I think you have to ask yourself the very hard question - do you love your h or are you addicted to him? There is a difference. He certainly sounds like a very damaged man, with a big raft of problems.
You might find the book 'How to get what you want and want what you have' by John Gray, helpful. The first two chapters are a bit offputting IMO, but the chapters on dealing with negative emotions, and understanding where they are coming from has been invaluable for me in accepting where I am.
