Not sure if this is a serious thread or a joke thread since the author is using a new account but I'm going to assume that it's entirely on the level. This problem is easily solved if broken down to it's core elements of which I see 4.
- Problem 1: The son is very anti-social. At age 20, he apparently has the people skills of a 12 year old so he withdraws into isolation, which is probably made easier and therefore worse in 2020.
- Problem 2: The mom wants to bring home female friends and possibly men for sex but she doesn't want to do it when the son is around which is all the time.
- Problem 3: The mom is starting to feel a sense of detachment and even revulsion toward the son.
- Problem 4: The son is not showing signs of improvement and the mom is losing patience.
These are all easy to solve now that they're separated so let's knock them out quickly.
1- He is adult age but he's still your child, ostensibly living under your roof. Tell him once and only once that he needs to start doing 'something', if he actually seems to be taking care of it, do nothing. If he keeps sitting on his ass, proceed. Take away his television and video games until he starts doing something. It doesn't have to be something grand but literally anything. If he started by going out to walk for 1 hour in the morning and later got a part-time job as a clerk in a store, even if he was getting complete shit for pay, that would be enough to jump-start his development up to where it should be. The key is you cannot threaten him with this, you have to do it without warning once it becomes necessary. Expect strong resistance but if you back down, you have failed.
2- Bring the men home and have sex with them even if your son is at home. He will no doubt hate it but he's an adult and he's living in your home. If he doesn't like it, he can work harder and get his own place (He won't).
3- This is the only serious problem. The bond between a mother and son is one of the deepest and most sacred bonds. Once broken, it's pretty much impossible to restore. The good news is that it doesn't break through "trauma" or petty incidents. The mother-son bond has to be eroded over time via loss of respect, growing disappointment and festering resentment. Basically, it's a slow process but once done, it's fucked forever..... you can fix this by getting him off his ass, as I had mentioned but also do your best to NOT resent him for messing things up so bad.
4- Sooner or later, you (the mom) are going to hit your breaking point. As long as you keep your cool and make sure he's moving forward rather than backward, there is nothing to worry about. Right now there is concern because he's just stagnating, but once that changes, the embarrassment and frustration will decrease and eventually disappear.
......
So tldr =
Tell him he needs changes. Take away his stuff until he does. Sex life at home even if he dislikes it. Don't wait or you may permanently lose your bond with son.
Oh yeah, and don't have sex with your son. Ignore the doujins, caption gifs and erotic stories. It won't help.