Te thing about the couples counselling, Filly, and the preposterous advice the counsellor gave you, and the attitude your OH (not DH, I think) displays when you're there and drops when you're not, is that couples counselling is not the right approach for your situation!
Couple counselling is based on two assumptions: the first is that the couple are deeply in love and just aren't communicating well; the second is that both parties are committed to making the marriage work. Now, while scraping and re-painting a ship's hull is a worthy enterprise and one for which people train and specialise, it's no help at all if the name on the stern is Titanic and the passengers and crew are jumping ship and heading for the lifeboats!
I think you can safely dump the couples counselling and find a good counsellor just for you, to help you understand and get through this mess strong and intact.
Your OH's working assumption appears to be that everything is your fault and your responsibility from start to finish, even incorporating a bit of invented 'history' when he couldn't trust you because you were working away. I'm assuming he benefitted from the commitments you made to your successful career? You don't seem the type to have had a separate bank account...
I don't think he wants to fix things in any meaningful way. He doesn't seem to have accepted any responsibility for his own choices and behaviour, let alone the impact they have had on you. It's all about him, isn't it?
Until he is honest with himself and you, he is going to continue to play the victim here, though assuming the pose is clearly taking some weird contortions on his part. As long as he is the victim of his sage, you and OW too, are cast as traitors and his oppressors.
You don't have to accept his version of reality nor live in it, with or without him. I suggest it's high time to look at things from your point of view, consider your story, inhabit your reality and focus on what you want and need. He's been binding a big bundle of his dirty linen to your back and you've been struggling to lift and move with it. You can just put it down, you know. It's not yours, it's his.
You are entitled to be angry and to talk about how his betrayal has affected you for as long as you want. He is not entitled to silence you on the subject, nor to tell you how your hurt and anger impact on him. He caused all this, after all. All of it. You don't have to listen to him moan about his wrecked life if you don't want to.
Think about when and how you will tell the children. Do it before he does!