you still need him to be as right as possible if you are his sole carer - in hospital, there are many looking after his care needs. i couldn't cope with my husband (even as a psych nurse - and I really felt I failed him) - but getting sectioned in hospital was the wake up call he needed and now he takes his meds like a good boy; attends appointments and therapy etc., whereas he didn't before and was chaos on legs. when your son has recovered, he will not blame you for this admission. you have to be tough on him and tell him it is down to his behaviour, illness and his management of it that is at fault - he is 20 and adult enough to take responsibility, mental illness or not.
i have psychotic depression and know the consequences of not taking meds ; drinking loads; smoking dope or no getting any sleep etc. there is usually a reason people get unwell (triggers) and he needs to sort these out in order to remain well. if he is still struggling with his diagnosis and/or angry about what is happening to him, this will take some time. he does need to work at things, though, and engage with mental health workers properly when he is discharged - you need to make that a rule if he is going to continue living with you. he needs to hear this and manage the illness....not the other way round. i still work full time, care for my hubby and i have also got a 19 yr old son to contend with. it works for me because i look after myself, do the things i want to do and don't care if people have an issue with me being unwell. you can just get on with life if you want to.....and you may have to try and help your son find his path through life, feeling ok about who he is even if he has an illness. take care x