Just to be clear, you are talking about forgiving yourself for past behaviour, not forgiving others for wrongs done to you.

You ask some good questions B_C and it's nice to see you in this space again.

It reminds me a little of Step 9 of AA's 12-step program that involves making amends to others and understanding that making amends is not exactly the same as asking for forgiveness. It's also about showing intention to do no further wrong.

(Mind you, I'm not an AA expert. There's lots to learn from AA programs and writings on line, and they offer some answers to your question: "What does it mean to forgive?")

You say

but I've really done some nasty stuff that has hurt a lot of people, including those nearest to me.

If those people still love you, perhaps they are waiting to hear from you. It seems to me that it would be hard to sincerely forgive yourself without first acknowledging to the other people an awareness of the pain you caused them and a realization that they may no longer trust you.

Your hope is that they will one day see that you have changed direction and are worthy of their love and trust.

What does it really mean to forgive yourself?

I'm not sure we ever really can or should totally forgive ourselves. But I think we can and should acknowledge wrongs done and take a new path.

Edit: We forgive ourselves by realizing that when the wrongs were done, we were the person we were. We had the needs, the pain, the awareness that we had. Now we are addressing our past deficits. We may not totally forgive ourselves, but we accept our past self, a self reacting to everything we faced; and move towards our reconstructed self, a self that considers choices before reacting.

I'm not sure if that is as clear as I'd like it to be. May edit again.

Sentence yourself to some kind of community service as a way of showing the sincerity of your new path.

How does that change your relationship with yourself?

It depends on what one's current relationship is with one's self. What is it like now? Do you give yourself a LOT of leeway? Do you make a million excuses for yourself? Would you trust you?

lil is wise, and gives sage council.

Personally I have struggled with self-hate for a long time. Then I was upset at myself for hating myself.

When I started being mindful, and when I started accepting, just a little bit, that I might actually be allowed to be loved, I started to forgive myself. It didn't happen quick, and I still have to work on being forgiving, but it is possible.

Now, when I make a mistake, forget an assignment for school, burn some food, spend too much money, etc. My first response isn't 'You idiot, how could you be so stupid!' or 'Greedy, weak willed bastard, how could you do that?' Well, it is sometimes, but less of the time than it used to. My first, and healthier response is instead 'You are just as human as anyone else. You are allowed to make mistakes. You wouldn't judge a loved one so harshly as you judge yourself, so why would you judge yourself that way?' and in recognizing that, also recognize that if there is a way to make right what was wrong, to do it, and happily.

The reason that I judged (And still judge) myself more harshly than I judged the mistakes of others, because I did not have the same love for myself that I did for others. I also hold myself to a higher standard than I hold others, but that's a separate issue.