You are making the pretty big ASSumption that he KNOWS why he did it! LOL!!!
Maybe a better tack to take is simply to start talking about what directions you both would like your new R to be going. You know the answer to why the affair started - because isn't it the same for almost every spouse here? He got depressed and/or freaked out about growing older, the OP was available (and/or scheming and manipulative), and the WAS was feeling unloved and unappreciated at home. The excitement of the affair gave them a dopamine rush that temporarily relieved their depression or anxiety and they mistook it for love. Same old same old story - you'd THINK people would be more imaginative, wouldn't you???
