Life as we know it

My son's father has decided he is a parent. Not that he has lived with my son for the past 15 months, he quit when his wife and my son got into an arguement. He did not stand up, he made no plan, he threw my 14 year old son with Aspergers to the curb, no coat, no ride, just abandoned like an old chair.
My daughter snuck him a bus pass, and he found his way to my house. I took him in and for the last 15 months we have supported him through therapy, one huge fit of anger, a trip to the hospital, the police, and his having to learn how to adjust, and now my ex has decided he is a parent.
My ex won't call the adults and talk with them, or send an email without threatening them. He actually yelled at my son, and then my poor son, who was trying to talk to his father actually spent 20 minutes begging his dad to calm down, and then 15 yelling at me because I wasn't willing to be yelled at.
How do you become a parent without any knowledge of your own child? How do you lie to the lawyer, and god only knows who else, about how great you are at parenting when your 13 year old daughter is up at midnight?

My son needs stability and I want the best for him. I want the best for my children, and how can I supply these and still allow him to see the children? I want to keep my sanity.

Threats

Today could have been great. It seemed like it was going to be okay. Day 6 of a med-less child, and he is finally starting to come into the normalcy, but of course, I got my hopes up again.
Alex finished the night with a fit of ugly temper, asking me what I was going to do and I finally lost it. I mean really how much stress can a person live with?
My husband doesn't have to, he gets to go to work, he spends his nights not fighting with teenagers, not being afraid of psychotic exes, and mostly not living the insanity, and then he threatens me with divorce, because I finally have had enough. Really, you are going to threaten me, grow up, I spend all my time building bridges, and he decides to threaten to leave. I hear this all the time from someone, Josh is going to leave, then what am I gonna do? I hate to say it but I truly hope he does so he can see how good it is here. A 17 year old who threatens, ooh big fear, maybe you should worry about graduating first? Alex threatens to join the military and when you try and explain the reason he can't he threatens to move out and go to another country and show me he can be in the military. I wonder if it would cause an international incident? He talks about becoming a dictator all the time. He tells me how great he is doing and then he tells me again, again and again. Do I seem angry, I am cause sometimes you need a little extra support and I guess i need to find someplace where i can get the support i cannot get at home. 
  I love them, but sometimes, when i am tired and my head is throbbing, and my arm is on fire, I just need a little help. Today was that day...