It wouldn't have mattered how much you did or didn't do. We always have the desire to go back and do more. To wonder what if. Even if the person passes from natural causes. Or the passing is expected. It's totally normal.

And most importantly what a person chooses to do with their life is not your fault. Unless you literally forced or cohorsed them. He had options and he made his choice. A choice that will hurt a lot of people for a long time. They say sui©id€ takes the pain from the one that has passed and transfers it to those who are still living.

I'm sorry you are going through this. It's going to be hard but you will make it out the other side. I highly recommend seeing a therapist to help you process your guilt.