Multiple Personalities Support Group
Dissociative identity disorder is a diagnosis described as the existence in an individual of two or more distinct identities or personalities, each with its own pattern of perceiving and interacting with the environment. At least two of these personalities are considered to routinely take control of the individual's behavior, and there is also some associated memory loss,...
I've recently been going through my own episodes of DID (ironically started in October for me too) that came out of nowhere and it was due to forced spiritual harassment that caused a spiritual awakening and hyper sensitivity in me. I am very much a straight male that has had a female alter try to dominate me. Among others. Even briefly gave me the odd fetish of wanting to be a woman, sexually. And I'm very much a straight male protector and thankfully I haven't gone as far as him. So, this is eerily familiar to me and I feel your pain and perspective.
It's actually 7 spirits trying to invade me, not knowing how strong will minded I am and I keep onto my core tightly! At the beginning they tried merging but I regained myself with spirit work after isolation and meditation. I found my 'true' self. Psychedelics/marijuana do NOT help it either. It amplifies it with false feelings of contentment. So, if he dwells in any of that, try to make him stop...
Again take my advice with a grain of salt or research it some more yourself, but my suggestion is to try secretly putting Black Obsidian, Rose Quartz, and Amethyst underneath his pillow at night or in his pillowcase and see if they "un-merge" gradually. Or if you two aren't living together; steer him in the direction via gifts unknowingly wearing said crystals as jewelry/pendants.
The fact that he doesn't want to see a psychiatrist prior such a huge life-changing event puts a big large red spiritual flag in the mix in my humble opinion. So, expect retaliation with trying to sway his mind, every which way.
Best of luck!