Respecting Boundaries?

How do you and your SO handle boundaries and respecting it? Not in sex more in conversations. We argue and he always brings up shit I did in my past and it literally boils my blood because I'll tell him to stop and he' LL go on and on about it and we've had discussion on letting go of things and when I bring up stuff he does he accuses me of never letting shit go. I'm getting so fed up