@selzero I have met too many people who try and hide their shittyness behind mental issues.
Which brought me to the simplest explanation:
"Your mental troubles may very well be an explanation for your behaviour. What they are not is an excuse!"
I then draw lines, like you did, and I tell them to work on themselves. I even offer help, if I think I can manage that safely. And then they have a simple choice.
Some cross the line and are axed from my life, but some I am now really proud of because they learned and got better.