You are alive. You can do this. You have your sister, and you have the desire. As everyone on this board says, you only have to go through withdrawal once if you choose. You can get to the other side.
I am praying for you, and sending lots of positive energy your way. Don't think about what you have lost/will loose. Think about what you will gain when you take these first steps. And then allow the rest to follow.
Hang in there. We are all behind you.