Apologies and forgiveness

I'm not trying to brag here, but there aren't too many people that I've really dicked over in my life to my knowledge. I'm a  pretty decent person all around. The opposite is not true. I've been screwed over by many a person, sometimes, admittedly because of my own actions. But not always....I've been in a very nostalgic mood lately and thought about two guys, well, one mainly (the other was more of a misinterpretation or misunderstanding rather than a "dicking over") that I seriously hurt. They may not admit it anymore, but I know it's true. And it is hurting me now. I need their forgiveness - the misunderstanding guy replied right away with a kind response, which made me feel a bit better. I mean, both these incidents happened over 20 years ago. (holy shit). But it's the other person who's leaving a hole in my ...? soul? heart? mind? because I feel like I really need his re-approval and forgiveness. I don't understand the demanding need I'm feeling at all. It basically came out of nowhere. Hadn't thought of him in years til I saw a photo of some of his friends I used to hang with too. Then it hit me like a shit storm. I'm a total asshole. I would be devastated if someone did to me what I did to him. Not like I hadn't been tossed around like a rag doll (not physically, emotionally) over and over for years. And I endured some serious pain. And I know what it feels like to have your emotions played with - it's an awful feeling, like a snake constricting your heart, then digging its fangs right in the center, bursting your heart into a million little pieces. Not like glass or china that can just be swept up and tossed away, or hidden beneath the rug. No, these pieces are raw and bleeding and burn like hell when you try to pick them up and get your life back together...Maybe time does NOT heal all wounds. I don't think I ever believed that anyway.... so  this person I'm trying to apologize to is completely ignoring my pleas and yes, my FB friend request. I thought, maybe he didn't recognize my last name since I'm now married, but that's bullshit. So now I'm hurt and bothered by this time period that's long gone b/c I can't get the closure (forgiveness, or hell, at least an acknowledgment). And that's ridiculous. Several people have told me I need to just let it go -- I tried to apologize and patch things up. I know things'd never be the same but this guy was one of my best friends for a few years. But my buddies tell me it's not worth it - it's in his court. They say he's not worth worrying about since I've tried (I'm trying), but as you can probably tell by now, I have a very difficult time letting things go. Not sure why. Not sure about a lot of things in this life...I haven't yet learned the art of forgiveness myself. Though I have forgiven a lot of people, I still hold grudges. Particularly against myself. How do I forgive myself for certain things, certain regrets? Yeah, Just Let Go. F that. I'd love to just let go. I just don't know how. Is it something you're born with or you learn? I'm trying...