I would tell his wife, or the HR department. I know it seems a bit forward, but if he’s coming to you for help he might be looking for ways to talk about his struggles. I was in a similar boat and my friend reported me to guidance, and my parents. I got in trouble, but I was never angry with the friend who reported me. It might tax your friendship, but it’s one option. Or suggest that you both tell his wife together? I know it’s ideal and helpful to have a third person POV so that the person being confessed to doesn’t overreact, at the same time its a personal issue, so boundaries are also important. I’m sorry if I wasn’t much help.