I would be extremely hurt to find out that my husband has “a past” that he felt he couldn’t share with me. Even though he put it behind him/changed/improved, it’s still a part of his life and something that helped him become the person he is.
I would never want to be too afraid or uncomfortable to share any past experience with my husband. Even if it’s something I’m not proud of…
I’m not saying that anyone who feels that they can’t (or shouldn’t) is making a mistake. But I daven that I should marry someone who can understand me on a level where sharing my past will not in any way lessen the respect and appreciation he has for me.
Notice that I said “husband” and not chosson. That’s because as long as it’s truly in the past, I wouldn’t be upset if my chosson waited till after we’re married to share it with me.