OK, I am coming at this from a completely different angle-and gently.
Yes, chronologically he is 19 years old. However, he is not emotionally at that age and it is actually sort of dangerous for him to be getting that amount of money every 6 months at this stage of his life.
No, you are not required to take care of him because he is an adult. You can however, let him know about opportunities he may have to complete his GED and it will be up to him to decide if he will follow through. Many high schools have programs for kids who never completed their GED-adult or not. They work to earn their credit. I belong to a support group of parents (mostly moms because we had a tendency to be the household caregivers) and a couple have adult children who have gone this route in order to finish getting their GED. So if you want-you could check into this. There are lots of community resources out there-if you contact your local human services department they may be able to guide you. Again, what he does with it is up to him.
OK, here is where I disagree with some people-gently. Many children reach the chronological age of adult but really are not adults. I don't think we should always push them out the door. Like you L2L I was out the door as soon as they handed me my high school diploma and never looked back. But I am uncertain this is where my kids will be--I have no way to predict that now. What I do know is they both suffer from brain trauma due to neglect and abuse. Being a child of a person who committed suicide cannot be a walk in the park and acdirito you probably know this--unless that has never been discussed. There may be a lot of stuff stuck in him that he is not talking about. Again, human service can provide you with information about where he can go to process this stuff.
Just like our kids need Alateen to process what is going on in their house to help themselves--other kids have other issues that need to be addressed so they can be helped. Having a mentally ill mother who left his world (and he probably thinks without giving a sh** about how it would impact him) may have left him with that swirling mass of questions. Sadness and confusion often manifests itself as anger because those other 2 emotions leave you feeling pretty helpless. Leaving you right now may be bringing out massive fear in him. Attachment is a big thing--and it is scary to let go. That does not mean you have to put up with his verbal abuse. However, if you can you might want to provide him with some resources he may or may not use.
Also, do not forget what you have done for your son. You gave him a mom. Maybe not his first choice for a mom--but he is going to just have to realize YOU ARE IT. There is no other mom for him. He cannot go out and shop for another and he can't make your daughter return to him. Have you ever had this conversation with him? That is why I asked about therapy. My kids have told me I am the last resort when it comes to who they would have wanted for a mom. First is their birthmom, 2nd someone in their birthmom's family, 3rd someone from their country and last-someone from another country (that would be me). But I have told them both-this is what you got and you know what. I am the best mom you could ever have. You may not feel like it right now but I am.
I can tell when my children are yelling at me and when they are yelling at their birthmoms. I actually bought dolls to represent their birthmoms and in the middle of a rage directed at me have handed them their doll and told them to tell her--because she left them, I have not, and never will. My kids are 5 and 9.
This may not be it at all--but if it is, he needs to move through it so he can get on with his life.
Good luck. My heart goes out to you. It is hard to have a child who is suffering so deeply and directing all that hurt at you. I'm keeping him and you in my prayers.