Sorry to hear you’re going through this op.
I know a lot of people on here are saying depression, but IME, you can only offer so much help and the person also has to help themselves.
There is no excuse for him telling you to fuck off or for throwing things and I would consider the safety of the rest of the household in case he is likely to ger worse.
He needs to start acting like an adult. If he doesn’t want to finish exams, fine, don’t force him. A PP made a good point that you can’t really tell a 19 year old man to go to school. But then he needs to get a job.
I agree with the other posters about removing his internet access. Change the password daily and give it to the other kids. Explain only well-behaved people get the wifi in this house and if he wants wifi, he can either improve his behaviour or he can get a job, move out and pay for his own wifi.
Stop doing his laundry, and definitely stop taking him to rugby. I personally think it’s embarassing that a 19 year old man is getting lifts from his mum to his hobby. He needs to make his own way there. Or as a minimum he needs to pay for petrol.
I’d also stop cooking for him tbh. And literally stop paying for anything. Is his dad really giving him money for everything including rugby?
When you do these things, if he accuses you of being a shit parent:
-Tell him you love him
-Ask him if there is anything else you can do re mental health support, support looking for jobs etc
-Remind him that he is an adult and therefore he needs to be in education or get a job and it’s unacceptable for him to demand this lifestyle for free.
-Remind him that you will be expecting the same of your other DC once they reach that age
-Offer any help again re mental health finding a job.
-Also offer to help him find somewhere else to live if he is unhappy here, but obv he will need to pay for it.