???
"Did anyone find going to counselling helped to understand why your partner cheated?"
@kimmillie didn't ask cheaters; the question was for those who'd been cheated ON. It's a sad fact that there are always, always, ALWAYS a lot of betrayed people to give advice or commiserate.
I can't think of any reason OP would care if counseling helped the person who cheated.
@kimmillie, I'm so sorry he has done this to you. It may have been 6 years ago, but for you, it just happened.
Individual counseling will build your confidence and help you find your way through this. It will give you strength, support, and some tools to retain your control when having to deal with him.
As for the OW refusing to answer questions, I wonder if she realizes her husband may still find out? If you decide during counseling to tell him, please take care of yourself and stay safe.