I wasn't unhappy for the bulk of our marriage. Neither was he - he even told me so himself on the evening of BD. It was only the last 18 months or so of it that was less than stellar - and all that time I thought it was only because he was tired and stressed and under the hammer.
I think this is the reason I have found it so hard to move on. To deal with this I have focussed as much as I can on those uncomfortable 18 months. As you say - reminding myself of those horrible, heartbreaking moments is great aversion therapy. Would I want to do that again? No...freakin'...way!