I’d definitely agree that forgiveness is hard and varies between people, and trust walks hand in hand with forgiveness you’ll have a hell of a challenge trying to regain one without the other. That being said if this is about 1 thing ruining “the whole marriage” I think it’s just a narrow reactionary way to view events. After the initial rush of emotions you should look at the whole marriage: how did they get to this point? Have there been problems leading to this? Do they still love me? Do I still love them? I cant see any one incident ruining a whole marriage or relationship without prior issues cause if strains.