How should a single mother deals with her 23 years ...

Frankly, nothing. He has his mind made up that you are the villian and no matter what you say or do, until he comes to his senses and grows up, you just have to ignore his derogatory comments. He is obviously very insecure and his life hasn't turned out the way he planned and he has to blame someone for his own ineptitude, so when he says these things just tell him you are sorry he feels that way then drop it. It will do you no good to argue with him, as a matter of fact it sounds as though he is trying to provoke you into arguing with him. He's angry with himself and he wants to make you his scapegoat. Don't let him do it. He knows the things he's saying are untrue, but his purpose is to make you as miserable as HE feels. It's so sad, that when people screw up their own lives they can't take responsibility for it. They always have to blame someone else, and it's generally one of their parents or both. You might think deep down he's a good kid, but if he were really a "good kid" he wouldn't be blaming you for everthing, that in his mind, he thinks you did or did not do that brought him to this point. I would suggest that you call a councelor or therapist and go in and talk to someone. You need to get these negative barbs that He's throwing at you out of your system, and to realize that until he does come to his senses, you are going to have to learn to roll with the punches or he's going to knock you flat on the ground. You need to unload on someone unobjective, who can give you a clear cut approach as to how to deal with it. Your son should come around eventually, but until he does you need someone to unload your emotions on, so you don't blow a gasket and possibly make matters worse. Good luck and I hope it doesn't take him too long to wake up. 

While an engineer in two disciplines, I have no formal training in physchiatry. Although I indeed have two adult sons, my answer comes from the perspective of being his supervisor as if indeed that were the case.

At 23 years of age, it's time for him to accept responsibility for his own actions as he begins constructing his own life. He must earn a life on his own merits. Mom won't be there to blame forever nor to support him.

So...face up, mom, and give him some "tough love" as his butt clears the door. If he is indeed a "good kid," he will be back. Above all, don't subsidize his disrespect by supporting him  - all, or in part. He badly needs to grow up.

Good luck and God bless you both!

I am only offering advice from my personal opinion's point of view because I am not a psychiatrist or in any profession along this line. From your message I am not sure whether you spent much time with him when he was growing up or not. If you did not then it is never too late to begin.