Can someone tell me how to just stop caring? Just turn it off like a water faucet?

I was married for 20 years to the most selfish man.  He was active duty Army when I met him.  After being married for five or so years, he was discharged from active duty and basically hasn't worked since.  He would go to school for this or that.  He would get a job and get fired.  He is an alcoholic and diagnosed bipolar.  I quickly realized that I had become his mother and not his wife.  I was taking care of him like I took care of my children.  So four years ago I kicked him out and filed for divorce.  He was devastated.  He cried, begged, and threatened suicide to get me to stay.  The divorce left me emotionally drained, feeling bitter and filled with anger.  He was a master manipulator to the bitter end, although it hasn't ended.  Because of our kids, he is still in my life, floating around the periphery.  Our daughter is 15 and while she knows what her father is, she also sees glimpses of the funny dad she loves when he is sober.  So I have tried to be tolerant and distantly friendly with him, but he sees these moments as opportunities to work on me.  I hate him, but at the same time I also feel pity and deep sadness for him.  I hate for my kids to see their father this way.  He lives in a rundown shack of a house.  He does not have job nor does he ever look for a job.  He just scrapes together money by doing drug studies or selling stuff  which he promptly spends on alcohol.  He does not own a car.  I have told him to apply for disability because I believe he does not possess the mental capacity anymore to hold any kind of meaningful employment.  Every piece of advice I give him is answered with you "I can't do it alone.  You have to help me.  I have no one."  His father died a couple of years ago and his mother has been gone for a while.  He has a brother who is in prison.  So he is constantly telling me that all he has is me.  He has asked me to "help him" buy him a car so he can "get a job" which he's been promising to do for 20 years!  He has asked me to let him borrow my car.  He texts me telling me he loves me and needs me.  The last week or so it has gotten really hot in our part of the country, nearly 100 degrees and he will not turn on his air conditioner.  So my kids drive by his house and see his windows open and call me because they are worried about their father!  When I told him I would not help him buy a car nor could he borrow mine, he went on a three day drinking binge and when he was out of booze and sobered up, he showed up at my son's house agitated, anxious, pacing the floors, and crying.  Then he started throwing up coffee-ground emesis and refused to go to the ER.  He left and called my son the next day saying he was okay and not to worry.

I've asked him to leave our kids alone.  Don't let our kids see him like this.  I guess I feel like the only way to protect my kids from this is to deal with him myself, but then that puts me right back into the middle of his crap.  I just wish I could be cold and unfeeling.  Just say I don't care.  I don't care if he has a heat stroke or drinks himself to death.  I don't care if he's passed out in his front yard or throwing up blood.  And sometimes, I can put it out of mind and I will block his number.  But it always creeps back in and I find myself upset and worried all of the time.  Worried for my kids, worried for that inevitable phone call saying something has happened to him.  I just can't turn it off!  I can't NOT care.  I feel like I have to worry about him so my kids don't have to.  It's my fault that he's their dad.  It's my fault that they have had to be affected by him.  So to protect them, I need to take care of him.  But I don't want to feel this way.  I want to be able to say you're on your own and leave me and the kids alone, although I know he won't.  I wish there was a pill I could take that would make me not care.  Mostly I just wish he would just go away.

I just really needed to vent more than anything else.  So there it is my anonymous vent.