The greatest act of forgiving

For many years, I was not able to forgive myself for the breakup of my relationship.
That happened many many years ago, when I was together with a lady.
We were together for 3 years, and I had proposed to her. We are supposed to get married in 2010.
However, just a few months before our wedding, she decided that it was time to part ways.
I was absolutely shattered.
I went through different phases of the break-up. At first, denial.
I tried all ways and means to salvage the relationship. But like a fish out of water, flopping helplessly around, the relationship was dead.
Then, I blamed myself.
I blamed myself for being too insensitive to her needs.
I blamed myself for being sarcastic and using hurtful words whenever we had disagreements and fights.
For the first time in my life, I sank into depression.
I only managed to slowly get out of it as I realized there were people around me who genuinely cared and reached out to me. My parents, my close friends and buddies.
I realized that to forgive someone is hard.
But the hardest person to forgive is yourself. It is never easy to forgive yourself and blame yourself for something which you have done/have not done. 
I have made mistakes, I have done wrong. But it is OK to make mistakes. 
If you are reading this, I want you to realize this, that we are all imperfect people.
There may be things that you have done or could have done in the past, to prevent something bad from happening. However, that is all in the past now. We can’t turn back time and change anything.
We can only live in the present and look to the future.
I have learnt to forgive myself. That is the first step of a very important healing process. I have learnt to be more mindful of my words, and I have made effort to spend more time with my partner and best friend. 
Is there something that you cannot seem to let go? 
Something that you cannot forgive yourself for?