Read other letters about this article
"I'm not asking for his approval of my past actions, just understanding and forgiveness. "
Why on Earth would he need to forgive you for something you did before you met him and which violated no trust you had with anyone? This is controlling nonsense and you should put it to him that if he loves you, he loves you for how you are now, and that past three-fer is part of what made you who you are now.
It's none of his business and if he can't see that, he should see his way ou the door.