We went to Relate last year, and it was the best thing we could've done.
There was no affair involved, but our marriage had been so bad during the previous 2 years and I felt an incredible amount of blame and animosity towards him.
I didn't think I'd be able to get past it. But as the sessions wore on, I found myself less angry at him. Nothing concrete happened, it just sort of lifted slowly, but surely.
It definitely taught us how to communicate better. Our councillor was briiliant, but if you're not happy with yours, be sure to ask for a different one.
Although my dh really was to blame for just about everything wrong in our marriage, there were things I did wrong. The way I spoke to him or the way I handled things, which the councilling helped us with.
We were also very good at leaving the problems in the councilling room and not dragging it out when we're not there. I think that helped, though your situation may be different.
Go for it. At least you can say you've tried everything if it doesn't work out in the end. And you're dh wants to go which is a good sign. Good luck xx