Lets say you finally decide to get married but before you do get married you wanted to come clean and confess of all the wrong you've done
So you agree no matter what eachother say you'll get married no matter what you just wanted to come clean.
You come clean and you say the worst thing you've ever done was like you got arrested for drinking and driving? and you didn't want them to know so you lied
Then your so said in highschool they had sex with a bunch of other teens and continued to have sex with them while they were in a relationship with you, but once they found out you were serious they stopped
I wouldn't make that promise in the first place. The whole point of sharing things like that is to see if the other person will accept you as you are, or not, and there's no way to force someone to be okay with something. They either are, or they aren't and then that's that.
I would get over the DUI, but cheating on me and not telling me? That's the tough one. It might depend on how many years it's been since then, and how much I value our relationship. He'd need to do some serious groveling and try to make things right, and I'm still not sure what I'd decide.