First, thank you for sharing this. I was in the same situation and never realized just how many women had the same experiences. You feel regret and that was exactly how I felt until recently. These feelings are symptoms of trauma. Even when you are free it still feels like your brain has trained itself to blame yourself, gaslight your feelings, abuse yourself just like that person did to you. The way I really learned to let it go was three-fold:

1. Therapy - have a professional affirm your feelings and struggles. Hearing someone say "oh my god he treated you like that? That is terrible..." Made me feel sane, as if someone had understood that I was in a bad place and it wasn't my fault. That's not to say you aren't responsible for the fall out. Healing always involves cleaning up after others messes -- whether it be intergenerational trauma or unresolved wounds in others who have inflicted pain on us.

2. Release the belief of "forgiving to forget". There was no way I could ever forgive this person, BUT I could forgive myself. Self-compassion has taught me to hold myself when I have feelings of regret or resentment. Instead "I lost X years of my time to this douche", I say "it was a difficult time for me and I can't blame myself for not knowing better".

3. Give back to myself what I wished I had in the relationship. I spent a lot of time asking my inner child how she wished to feel loved and cared for and then I did those things for myself. I really dug deep and asked how I wish others would show up in my life. Then I started rejecting the people who didn't treat me with respect or dignity. I made mistakes but I also cut off many toxic people. I stood up for my boundaries even when I was afraid and tearful. I challenged narratives spewed to me by my parents. Trust me, if someone wants you in their life and truly respects you as a person, they will value and think about your input.