Hi @Chinup
I'm sorry it is such an incredibly tough time for you right now. It's must be such a challenging time for the both of you. Caring for someone who is terminally ill can be such a mess of motions and difficulties. While i don't suffer from psychosis or any mental issues like that, I can speak about dealing with a terminal illness. I can be incredibly frustrating and upsetting for anyone to deal with, let alone someone going through mental challenges like your son is. I think it is important not to escalate anything with him. Try to stay calm and avoid arguing. I know a lot of what he say is unfair, but just try to be there for him as he struggles through. Telling him that you are there for him and that you can see how difficult it is for him will help him to see that you are just there to support him while he deals with so much in his life.
I can understand his resistance to taking medication or going to the hospital... it can just all get too much and feel a bit pointless after a while as he comes to terms with his future. Does he have a doctor or even a palliative care person you could speak to in order to find some safe ways to support him, especially when he is in these manic/psychotic states? Even one of the crisis lines may be able to offer you some advice as a carer. It is important to consider you own safety and mental health as well while trying to support him.
I think it's important to remember that you do have limits as to what you can cope with, just like anyone else. So while I understand how difficult a position you're in, it is still important to look after yourself as much as possible to stay in a state able to support your son as much as you can. Also, letting him know that you want to help and be supportive but your own health limits what you can do. Use 'I' statements so he knows you are talking about yourself and your limits rather than placing blame on him. For example, "I need to slow down a bit to allow me to keep supporting you." If he reacts negatively to anything, then just distance yourself for a moment rather than trying to reason with him as it will probably only make things worse.
So i think it is probably a case of being there for him, supporting him as much as you can within your own limits and distancing yourself when he becomes more antagonistic or angry. It may seem like you aren't being supportive, but you are doing so much and like I said everyone has their limits and taking a break away from him when it becomes confrontational is the best for the both of you as you need to stay strong to continue supporting him, and he needs to know there are limited to what you can do. Either way, don't be afraid to think of your own well-being as well and to seek help and/or advice where ever you can.
I wish you the best in getting though this.