He admitted to an affair. An affair by definition is a bad thing.

You can be poly and sleep with multiple people with the consent of your partners and it’s not an affair.

An affair, being unfaithful, cheating, etc. are all terms used for someone who has breached the terms of their relationship. We don’t need to be slow to judge because he judged himself by using those terms.

You have no idea what the situation in his relationship was like at the time. You don’t know how his wife feels about it, you don’t even know if she knew about it. Be slow to judge.