Let me ask, are you doing anything now to make your future self proud? I was pretty miserable for a long time too, and it wasn't until I got out of that particular dark chapter and did some good for myself that I was able to be compassionate towards past me. I know it is a bit of a chicken and an egg problem, but if you can start working on your future self, it becomes easier to forgive your past self. At least that's how it worked for me.

Peace, friend