Self-forgiveness is something I've been working on too. Its so hard when you know you have a capacity for cruelty, I'ld offer it's easier by getting sober, and growing for you.
Understand you don't need permission to love yourself, or any reason. The doubt that I, or those with BPD feel in terms of being worthy is a falsehood planted by fear, neglect, trauma etc. It isn't you, and doesn't have to be your inner monologue.
You don't need their forgiveness to understand you can do better for yourself and others
You don't need to prove to anyone you are growing, or healing. That can play into this performance for approval, and to avoid rejection but in your brainspace you could still be rejecting self love.
No one is going to celebrate your growth or validate you how you need until you discover what that looks like for yourself. That's not so isolating as it is empowering. You can be the eye of the storm. And in the end you live with yourself, so when you spend time alone, don't you want to be kind to yourself? Once you are kinder to yourself, its easier to be kinder to others since what we live in prayer; what we practice we become.
I truly hope this doesn't further add shame, I'm only sharing some frames from therapy and videos which have helped change my inner monologue this past year, and stop clinging to the past so much.
Forgiveness is a process, and ultimately I'm only trying to communicate you are capable of change and growth. And your actions in one moment aren't who you are wholly, nothing is permanent and ruminating may only lead to reinforcing this shame you are carrying.