@SJT63 I'm so sorry you are dealing with all this my friend. My heart really aches for you.
Sounds like Mr S's episodes/mania could be a bit out of control, either that or he's using his mania as a catalyst to act like a butthead.
I would say definitely a wise idea to talk to his Psychiatrist. I would suggest taking the time away from prying eyes, to write up a list of Mr S's recent behaviour and its effect on you as well. Take that with you as often it's hard to remember things to tell specialists in session, especially when things are so highly charged emotionally.
I can only speak from my experience but it's possible that Mr S needs to develop some more insight into his illness. If he is truly repentant of his behaviour when these episodes pass, perhaps suggest to him that it might be a good idea for the two of you together to sit down and explore his behaviour when things are out of control.
If you can mutually agree to explore and try certain strategies when he is well, there is more likelihood of him being able to control his rage when an episode hits.
Speaking as someone with bipolar who used to have those rage feelings constantly, for me gaining more insight into my illness and how it effects me has been crucial. Gaining more insight and accepting that side of myself has allowed me to really reflect inward and ask myself, okay how can I lessen the impact of these episodes on the people around me and myself. That's where the growth and healing starts.
As far as him acting out when he is raging and being worse when you don't engage him, try telling him calmly that you refuse to engage with him when he is being so hostile and then walk away. Keep telling him that, if calm doesn't work, be firm and confident and adamant that you will not engage with him when he is being disrespectful and hostile. Set a really strong non negotiable boundary and stick to it. And keep saying it over and over. Think of it as training his bipolar to recognise that you refuse to engage with it. When mania hits, it's hard to stay focused, but if you constantly repeat to him his behaviour is unacceptable eventually that message will get through. If it gives him pause to think, "gee yeah I'm being an a**hole" it will help him learn to control himself better.
When the episodes subside, that is the time to engage with him. The difficult part is to try not to blame him personally but place the blame squarely on the illness. And don't tip toe around calling it an illness, because he needs to realise he is sick and when he is sick his behaviour towards you is hurtful and distressing to you.
I cannot even imagine how difficult caring for Mr S can be. But I do know that there comes a point where as someone with bipolar, you have to take responsibility for your actions, bipolar driven or not. It is essential that you own your illness warts and all, and until you reach that point, sadly and unfairly the people you love seem to always be the battering rams.
I wish you well my friend. Sending you big hugs and support. xx
BB 🐰💙