What Should I do to Win my Fiancé' Trust?

Good morning ma, I have a very caring and loving fiancé but the problem now is that he doesn't trust me a bit because
of the past experiences he had with his ex.

I don't really know what to do, I don't cheat on him and he doesn't either.

Please advice me on what to do. Thank you

If he doesn't trust you, I'm wondering why he proposed marriage to you, and how you hope to live the rest of your life proving that you are not his ex or any other lady. 

Trust is not what anyone can prove because it has to do with a personal conviction and not by efforts of another, especially when you are dealing with an individual who is emotionally broken and weak. 

If he doesn't trust you, I'm afraid you may experience more pains and emotional torture loving him or living with him.

The choice is yours but I will suggest that you pause the marriage preparations and address his insecurities to avoid regrets in your marriage.