Hada, the point is that small mistakes are no one’s business as we all make mistakes. Large mistakes that are well known and can come back and bite you, should not be concealed if it might be considered a lie or a lie by omission by your future spouse and cause sholom bayis problems in the future. Think about how you would feel if the shoe was on the other foot.
If c”v you were a girl who once hung out all the time in your youth and was actually OTD and ate treif b’farhesiah. Now as a mature young lady you are on the right track and have left all that behind you as foolish and childish and having gone through a very rough patch at the time in your life. Kol Hakavod and kudos for having the strength and emunah to turn your life around and become a true Bas Torah. However, there is a way of telling your future spouse about this time in your life in a non-problematic and non-confrontational way about how you have made tremendous strides in your life. In other words by talking about the positive influences in your life and the improvements you made in your journey of becoming you. Sometimes, it might be necessary to have this discussion together with the Rav who knows you the best so that he can pave the way for understanding so the young man does not get scared off.
But what if this is not disclosed and the gossip mongers get to him after the marriage is sealed. “Did you know that I your wife used to be friends with my sister and they used to eat at McDonald’s?” How do you think your husband would feel if he was hit from left field with such a revelation? On the other hand if he had the knowledge he could combat that yenta with “B”H isn’t it amazing how she turned her life around? And how is your sister doing?”.