I think you are describing a man who has been growing up. This all started when he was only 12 or 13. Heartbreak at that age can be devastating, it’s true. But it’s also the time when people start to learn about relationships and how to handle rejection. The fact that he was still “recovering” from the breakup when he was 18 or so says to me that he didn’t have the inner courage or the external supports to try again until he met you. He was therefore behaving quite immaturely, thinking that controlling you was the way to keep himself from being hurt. As he discovered, trapping someone doesn’t make a good relationship. In an effort to be honest with you, he told you about something he did when he was an immature 13 or 14 year old. Instead of being sympathetic with the young and confused boy he was, you are holding a 20 year old man responsible for what he did 7 years ago.
Please take a deep breath and ask yourself: Do you really want to be held accountable for everything you did when you were young as well? Most of us do things when we are growing up that in hindsight look pretty stupid. But it’s part of growing up.
If he has evolved into a decent, honest guy and you really love him, you owe it to both of you to see him as he is now instead of how he was as a young teen. If he learned from his mistakes and loves you as much as you love him, then you can drop the distrust and depression.
I wish you well.