I'd like to join Sophie_M in welcoming you here. Trying to live with a partner who has delusions is terribly hard. They can start as semi-reasonable suspicions and develop to the point where anyone can see they are nothing like reality. Trying to deal with that is fruitless, as your partner realy believes the matters concerned and no amout of logic or reassurances is going to work.
It can make one feel very lonely at times wiht the person you love so far off track and you alone, particularly if he is at odds with his family due to his beliefs and behavior.
Now you have the additional worry that something you say might start an angry extended outburst, stress for you all the time and deeply upsetting when the outburst comes and keeps on going.
Holding yourself in check and trying not to be angry , making allowances for is conditon, is not something that can go on for ever. If he drinks and takes drugs he is in all probability making his conditon worse, and if he has been given medication the combined effects can render the medication useless, and the result very unpredictable.
Irrespective of the actual diagnosis his behavior seems to have reached the stage where I think you need medical advice. You need to see the doctor yourself anyway as your own stress levels will be though the roof, and if that goes on for too long you can become ill.
I'd suggest saying how you feel, what is happening and about his drinking and drugs too. It will take an extended consultation. See where you go from there.
In many states there is a Crisis Assessment and Treatment Team you can call when he is obviously raging and in distress
A list for each state is here:
Some states have a better service than others, but it may be worth a try when his illusions become too far out and he has these outbursts.
You can do is go visit his psychiatrist. You can't ask questions but can give your own detailed account. That way the psychiatrist will at least know there might be some doubts about your partner's story.
Another problem is to ensure he takes his meds. In the right circumstances they can work well. Here however you have drug and alcohol in the mix.
The links Sophie gave you are good ones. Use them. In addition if you have nobody to lean on can you be in contact with your parents or family in the UK? Being so isolated is very hard.
You are not alone here and always welcome