I was in despair that someone ruined everything over nothing. They continue to ruin their life and everyone's around them.
That sounds terrible.  What can you do?
Not much. If someone wants to destroy themselves and everything that is ever good, you just hope they stop. All you can do is put boundaries up and try not to let their crap take you down too.
I definitely agree you need to set up the boundaries.  Make sure you keep that up for the sake of everyone involved.
I am, don't worry! VERY hard when you have loved someone so, but I am. They are not staying here anymore. So sad when some just don't care.