My (22F) fiance (23M) used to be not so great. Now he is. But the damage is there.

My partner used to be very inconsiderate, sometimes mean. There was a time where he crossed a boundary of mine which hurt me very very badly.
Ever since, we’ve grown and he’s become wonderful.
But I can’t shake the feeling of being unsafe or secretly wondering if he loves me as much as he says he does, even though he tries his best.
I’ve tried to talk about it but it seems to be, brief, and lack substance from his side.
I feel like this issue is of me not being able to trust as much as I used to and carrying the past into the present, and him not giving me the emotional depth I need. But I feel like an awful person.
My mental health has dwindled horribly, and I feel like it’s unfair to both him and me.

Aside from my own personal experience, have any of you ever faced an issue like this, and what did you do?