I went to couples counselling after cheating on my wife 15 years ago. It was a ONS but I'm not trying to minimise it, it was the worst thing I've ever done. The counselling kind of worked & didn't work.
It really helped to have an appointment once a week at which all the issues got discussed, because it sort of sucked the poison out of the rest of the week. Knowing we had Wednesday afternoons meant we could cope better with the rest of life, work, bringing up 3 DCs.
But it didn't resolve our conflicts, we did that ourselves. The counsellor kept talking about our needs, physical & emotional, but I wasn't happy with that, seeing as the whole reason we were there was that I'd gone off and satisfied a need with someone else. I told the counsellor this, but she just kept on. I think I know why she took that approach, but it was pissing my wife off hugely and eventually she stormed out & I don't blame her. We used to have massive talks in the car after the counselling sessions, and these were far more useful. Tbh we rather united against the counsellor, which seems ungrateful but it helped, paradoxically, the sessions were a catalyst for the real hard talk we had to do.
I believe cheaters fall into two categories, fools & bastards. I was an almighty fool, couldn't see what was happening (person I cheated with was an old friend in trouble, getting divorced, I fell for the whole rescue scenario), my wife could but I wouldn't listen. Others plan their cheating, do all the lying and hiding you have to do to keep an affair secret.
I'm so sorry your OH has done this to you, it stinks. All I can say is, we survived but oh my god it took so much honesty and effort. What I realised after a few weeks was, I needed to be punished. There wasn't much point banging on about WHY it happened - I remember my wife raging at me because I was handling the aftermath of it worse than she was. My 'job' at that point was to shape up, try to be the best husband I could be and do a ton of work on the house.