Antlers: It's kind of like you're listening but you're not hearing. But here goes:
1. Take charge. You are the adult here. Make a plan for all 3 kids. Something they would like to do. Something fun. Then tell them when and where and that you'll pick them up. Ask them to RSVP by ... If they decline - that is their right but take son anyway.
2. Make a list of Positives. All the good things in your life. Let me start for you. 1. Career 2. Son lives with you 3. Health and so on...
3. Use the Stop Sign technique I told you about. When you start thinking about ex - put up your Stop Sign and redirect your thoughts to something. Anything. Put on some music. Read a book. Watch a movie. Play a game with son. Stop thinking about it.
4. Get up in the morning and say "Only for today I will" ... (suggestions include - not think about ex, only do things that make me happy, concentrate 100% on son, make a small effort with daughters).
5. Happiness starts with small steps. Small steps do become bigger strides. Do something nice for others and you reap more back to you. And your focus becomes different.
6. Recognize what is inappropriate at this stage. You and your wife are divorced - she can date whoever she wants to. Or move him in. Or marry him. At least he didn't cause the divorce. My husband was running around with OW for months before I even knew. Not just an infidelity - those 2 went everywhere together. It was horrifying! He moved straight from my house to an apt with her and called it their Love Nest. And I got PAST it! By 3 years I was a lot past it. You need to work on this.
7. Listen. Be Proactive. It really strikes me that you keep beating the same drum when you are in counselling and we are all telling you how you can work on yourself. Then you tell us once again about her. We don't need to hear about HER and her opinion of counselling. We need to hear "How's this been working for you".
8. One of the problems here (and with many people on the board - notably more men than women in my humble opinion) is the need for an "instant fix". And it does not happen. No one wants to feel miserable but the longer you put off making the changes - the longer it takes to start feeling better.
I will give you credit for making some changes that are helping. These include exercise, counselling and spending time with your son. But you really need to work on redirecting your thoughts and also on steps to improve your relationship with your daughters. In whatever ways that takes.
Why is your son so angry with you? Are you sure he is angry with you or just angry with the entire situation? It really helps to know in order to help him learn to deal with his hurt and anger as you live with him and you need to be consistent in dealing with it and helping him.