forgive and forget

It's one thing to accept God's forgiveness. It's hard, but at the same time, it's easy. You don't have to jump through any hoops, you just have to be sorry and repent. God has forgiven you.
It's a completely different thing to forgive yourself.
How do I forgive myself for something that will be with me for the rest of my life? Something that will not only effect myself, but effect another person? How do I forgive myself for something that has changed me for the worse and I can never change back? I realize I'll never forget it. It's burned into my mind for the rest of my life, and in a sense, I've accepted that. But at the same time, I haven't accepted that because I can't forgive myself for that very reason. It is always the first thing I think of when I lay down to sleep, and it keeps me up for hours. I have screwed up this time. Really really screwed up. I've been living with this guilt for months now, and I have no idea how to get rid of it. I'm so full of self-hate and regret, and rightfully so! But I'm miserable. I can't stand this any longer.