the "should haves"

I guess I am just venting, please forgive me for spelling errors.

A friend of mine, only now I don't think we can call ourselves acquaintances. Loved life, lived well and always dreamed. She has been battling depression for the past few years, and I regret to say I wasn't able to handle the emotional stress and broke things off in an extremely immature way.
After breaking things off I felt relieved, happy, and like I didn't have to worry about another person completely depending on me to be the emotional support her family should have been. You see, for 3 years I was her only friend. After feeling all these good and happy emotions, I decided it was finally time to follow my dream and move to the United Kingdom.
Her sister just contacted me and this once vivacious, happy, beautiful, witty, dreamer of a girl has now fallen into doing hard drugs.
If I would have stayed could I have prevented this?
For the last two hours I was prepared to hear that she attempted suicide again, or worse, that she "succeeded."
Is this worse? I feel like it is.

I have been playing with this idea for a long time and I think that the events of this even has pushed me over the line..
I want to start "What It Should Have Been."
Writing short stories replacing the life that was taken away.
Miscarriages
Murders
Suicides
Anything that I just honestly wish I could have given them if I had been the writer of their story.

Please give me your opinion on this and/or any advice on how to go about this.