Oh Lil, it sounds exhausting. I was looking for a comment I think you made..about how hard it is to have them home. I couldn't find it, so maybe I imagine it, but I will say...yes, it is much harder when their every stress, every misstep, every mood swing is in our faces. That is hard with easy child young adults, and it is hard with difficult child's. There is a difficult transition with young adults when it is just hard to live in the same house with them...that means it is time for them to leave! It often happens at the end of high school when kids, easy child, difficult child, or other, are leaving for college. those are the ones (like me) who don't cry when they leave. It was time for easy child daughter to go. We fought and wrangled and rubbed along and it was time for her to go.
SO lived with his 19 year old (then 20, then 21, then 22, then 23) year old daughter when I met him. She is a nice young woman...now. Then she was supposedly in school to become a nurse, but was really taking intro course after intro course at community college, after 4 years doesn't even have an associates degree to show for it. She took college loans and lived for free and used the loans for parties and clothes. She was AWFUL, and I thought she was a difficult child. Now I think it was situational, transitional. He sold their house, she had to move in with friends, and she has become the lovely responsible working, self supporting girl she is now. Every little thing he hung on to as her parent (keeping her on his cell phone service and car insurance to save her money...she was supposed to pay him her share but sometimes did and sometimes didn't) hurt her. He had to cut the strings, which was a fairly ugly process, and then she flew.
I know your son is not his daughter, it is just food for thought, and some comfort that the exhaustion is a normal transition. I know he is your only child, so this is a new process for you.
You commented that you feel bad about posting because your situation is less dire than some of us...I had two thoughts about that...one is, if you feel desperate and despairing and unsure of your parenting and your kid is off track (all of which apply to all of us, including you) then welcome to our club! Of course we welcome you here, and listen with all our hearts. The second is...there was a time when our kids were like yours. Cedar, REcovering, Child, me...there was a time when our kids were incomprehensible, off track, but still home and we we still trying to save them...they don't go straight from childhood to drug addiction or homelessness or street living dual diagnosis badness. I don't know where your boy is heading, but you are right to be vigilant right now.
I think I said this to you before, and I hear it in Child's post to you too....try to step away. You are in soooo close, you know when he is late to work and how he feels about it, where he goes, what he spends, how he gets there...its a lot for you to try to process. Its too much.
But if I step in now, even when it APPEARS that he is trying to change his own situation---I will rob him of the learning HE MUST DO---he must do---he must do---in order to become a functioning, contributing adult.
They have to manage on their own to have any self respect. In learning to manage on their own they will flub and fall, sometimes gruesomely. But they will definitely fall if we do it for them.
An earnest neighbor left me a nervous voicemail the other day...he said he had seen difficult child and talked with him, that difficult child had asked him for money for a phone and that he had almost given it to him but had decided not to. He was sort of apologizing for that decision. I called him back and told him NEVER to give my difficult child or anyone else's any money..that everything that anyone does for him that makes this life he chooses easier, that supports his behavior and decisions in even the smallest way, keeps him there that much longer. He has to hate his life enough that it is easier to change than live it.
he may get fired. Or he may quit. And if he does, he will have learned something from this, and he will take that to the next job.
This is true and important. He may get fired, or quit. This is not the end of the world. The story here is loooong, with lots of ups and downs. Don't pin your hopes or happiness on the short run, the success or failure of this version right now. IT is what it is, you can't change or control that. More things will happen, more things will come along. Try not to burn yourself out over him, his job, his life, right now.
Hugs, and as Child said, no judgement here.
Echo
As opposed to an actual reason. The reason would be he messed up and lost his transportation and didn't find another way to work and got fired for absenteeism. 
