For me, it took a bit of a disaster (my first marriage ending) to get into therapy. I had to get at why I kept having the same relationships over and over again instead of just jumping into the next one and watching it implode the same way all the others had. Forgiveness was a three part process for me.
Talking to my therapist began the journey of understanding where I came from. I needed an intellectual understanding of what happened to me in my childhood (growing up with an alcoholic mother and co-dependent father) so I could see that I behaved in relationships the same way at 35 that I did at 5: assuming I was not good enough, that I did not deserve to be happy, and that my feelings and needs were less important than theirs. I had been turning everyone I was in a relationship with into my mother, because it was comfortable and safe and I knew how to behave.
Second came the emotional understanding. I am good at getting things in my brain, but my heart often had a harder time letting stuff in (and why not, it had been hurt a lot by the very people who were supposed to make taking care of it their first priority). So feeling my way through this was the longest step, and the hardest. I cried a lot. But when my heart finally "got" that it wasn't my fault, then I was free to build a new way of having relationships.
And that was the third part. But before I could try out a relationship with someone else, I had to first have a successful one with myself. I had started the process with that emotional understanding of where I was coming from and what I had been doing, but now I was free not only to forgive myself for my past mistakes, but to accept that I was a good enough person to deserve love -- from myself, and from others. This part was about getting to know me - the "me" free of my childhood burdens, the "me" free to explore new ways of looking at the world. I spent a lot of time with friends. They provided wonderful mirrors to the best parts of myself that emerged. I wrote a novel! I decided to spend each moment IN that moment. If I was working, then I was working and not thinking about the past or the future or anything else that was out of my control. If I was at rehearsal, I dove in. Whatever I was doing, I dove in. I took care of nurtured myself, alone.
The final test came when I met someone with an alcohol problem. I got involved with him even though I knew better. We went through all the usual crap one goes through with an ABF. I think I needed to show myself that I really couldn't fix someone else. There was really nothing I could do to make another human being happy. And I got out of it when I finally understood that, and I never looked back. The old me would have beaten myself up to no end for getting involved. Because the old me was always looking for a reason to beat myself up.
Hugs to you.