Praise be to Allaah.
With regard to the past from which you have repented to Allah, may He be exalted, the fiancé or husband has no right to ask about it. And it is not prescribed for anyone who has fallen into sin to tell anyone else about it when Allah has concealed him, and he should not expose himself, Allah forbid.
If the fiancé or husband insists on asking, you do not have
to tell him about what you did before you knew him. Hence you made a serious
mistake when you told your fiancé some of what you had done. Rather he
should only look at you as you are now, and if that suits him he should go
ahead and marry you, otherwise he should leave you for someone else.
Now what has happened has happened, and you do not have the
right to tell him any more than you have already told him or what he has
found out himself. You can deny anything that others might tell him and that
could damage your image and reputation.
See also the answer to questions no.
112090,
83093 and
91961
But if he says he is going to divorce you after that, then
this matter is in the hand of Allah and intentions may change. “You (the
one who divorces his wife) know not, it may be that Allah will afterward
bring some new thing to pass” [al-Talaaq 65:1]. So ask Allah to accept
your repentance and to conceal your errors.
And Allah knows best.