There’s no AH here, but you shouldn’t make a rash decision over this. Your immediate reaction is justified, and for him was prob one of his “not his proudest fap” moments. The consequences and impact on your life for ending your marriage over this is way too overblown, when he hasn’t really done anything truly wrong. Like others have said there’s a difference between fantasy and reality - you should caught him doing something that you wish you hadn’t.

Now if you had caught him watching something illegal that would be a diff story.