He was/is simply jealous. He has hated himself for years because he couldn't find the courage to come out as trans and live life 'out loud' as a woman.
You are absolutely right that he was living his fantasy transition through you.
He became so angry/resentful at you disregarding his directives because, only slightly below the surface, your transition was *his* transition.
You were his 'avatar' empowering him to do, through you, something that he's convinced that he'll never have the courage to do for himself, in real life.
As long as he firmly believes that he'll never have the courage, he never will.
Your morbidly obese friend has has been eating his emotions, his hatred of his own 'cowardice', because that's how he sees himself, as a hopeless coward.
He's been well aware that the eating will kill him, all along, and secretly hopes for death to come, sooner rather than later.
I know what desperation feels like.
Your friend is in an abyss of self-loathing and abject despair.
When you're in a state of pitiful and incomprehensible demoralization, wishing you could just be dead and have it all over with, but are too afraid to commit a precipitous act of suicide,(proving, continually, what a "coward" you are), your acting skills become, by necessity, Oscar worthy.
When you refused to transition as per his exact plans,(from his point of view), you put the final nail in his coffin.
It's not your fault in any way. You just happened to be there at the time. He latched onto you for the aforementioned purpose.
Your friend is in a very, very bad place, but it's one that no one can talk him out of.
His dilemma is a trap that he,(so far), lacks the courage to get himself out of.
He cannot ask for help without admitting his deepest shame.
He is at a very high risk of suicide.
Looks like he's opted for a slow death by overeating.
Secret shame like his kills, in one way or another, an enormous number of people, every day.
Your dilemma is that trying to talk to him, to help him, could trigger such a panic in him that he succeeds, finally, in ending his misery.
I've been where he is, except that my weapon was alcohol and drugs, rather than food.
If you want to attempt to help him, I strongly encourage you to enlist some help from a mental health professional.
--weezi--💜🌈🙏🏼🦄🥳🦄🥰🙏🏼