Hi @ooxide. I have no experience of what you have gone through in your relationship with your mother but what I do know is that the mother/child bond is one of the strongest and it also works both ways.
Obviously, a whole range of emotions encompasses this bond. We can both hate and love our parents at the same time. We feel exasperation at some of their behaviour and yet often use their behaviour as a role model. It is a complete emotional omelette that is often hard to make sense of. We have lived with that person through our early years and made a lot of emotional investment with them. It is so easy, therefore, to feel the pain they are going through and then to try to find a reason for it. Invariably many take it upon themselves to shoulder some of the pain and hence the blame.
From an outsiders viewpoint, and going on what you have written in this and previous posts, I honestly don't think you can feel guilt at your mother ending up in jail. You say you place the blame on your leaving when you were in your teens, but looking back, do you think she would have travelled the same path anyway? If you hadn't left would it have been something else that tipped her over the edge? Was she self-destructing no matter what?
All speculation on my part of course but it's good to see that you and your mother are growing together again and I wish you all the best for the future.
You're not wrong; logically I know why people say that it's not my fault. It's not. The problem is that feelings aren't always logical, and the longer you hold them the stronger they get. It's vicious :(
I know it sounds very new age to say this but I have found Mindfulness to be beneficial in helping me cope with my depression. It enables you to let go of feelings and helps put them in context. Maybe something like that might help?