Ladyrider- what you feel is real regardless of whether anyone has direct experience of this issue. I have (long time ago) so have great deal of empathy for you. The pain is sometimes unbearable.
Looking back now I am sad that I wasted such a long time feeling angry, humiliated, hurt and of course the anger was covering the hurt. It's sometimes easier to be angry than to hurt.
To be honest (and I don't mean this to be critical) I don't think whatever your bloke does (or doesn't do) will be enough to assuage the hurt that you are feeling. I remember the feeling of wanting things back to normal but working against that was my continuing anger, and his guilt which he also covered with anger. I didn't know what I wanted - one day I wanted to know all about her, what they did etc., and then would start having a fit when he tried to answer - then the next day things would calm down before I was off again and more rows and accusations etc etc.
We parted for a while (he went to college some distance from home and rented a flat) and we used to write to each other. In that way, we could say what we honestly felt and I learned a lot by what he wrote to me, and how he wanted to make things up to me but didn't know how. It helped a lot as it meant we weren't shouting at each other.
The other thing (and I hate to say it as it is a cliche) time does heal. It used to feel like a football in my stomach, and then over time shrank to a tennis ball, then a golf ball, then a small bubble. Sometimes I took 3 steps forward and 2 steps back. I was lucky to have friends in whom I could confide. It does helpt to talk and I agree that CBT counselling could help.
It is something that you won't "get over" but it will shake down into something much more manageable over time, BUT it does take time. Be honest with each other, even if you have to write to each other. I used to get rid of some of my anger by just writing it down, in huge letters with a big black pen (only for me) - sorry I am rambling and not sure if this is any help.
Just to say I do sincerely wish you well and hope that things get sorted for you.