I’m so sorry- this is an awful situation to be in for everyone involved. I feel for you and your family.
I left home in my early twenties (I wasn’t very good at adulting yet) because my parents were very homophobic and emotionally abusive. It was really very hard. I did “ghost” them (although I wouldn’t have used that term) and haven’t spoken to them since. So I thought that I’d mention a few things to consider from the perspective of someone who is estranged from their family.
As others have mentioned, the friend in Boston sounds dangerous. Best case scenario? It could be another trans friend around their age that they met online interested in “rescuing” them. Friends like these get bored about 6 months into hosting someone when the no longer feel like they’re getting positive recognition for helping a wayward teen. (I read Ties That Bind: Familial Homophobia by sarah schulman or something like that and it mentions the lack of responsibility anyone feels for lgbt people- even other lgbt people. This has been the case for some of my friends and me.) They can drop a person and let them fend for themselves. It’s more likely that he’s being groomed (by a transwoman or another predator in the lgbt+ community or possibly even an ostensibly “straight” guy). It could also be a TiF that fetishizes gay men or that sort of thing, but in all likelihood it’s probably an older man. It’s definitely not a situation he wants to get into.
I think this is going to sound counterintuitive to you, but I suggest giving him more responsibility. When one person in any relationship is underfunctioning, someone else (you) has to overfunction. He needs things to take his mind off of the trans issues and taking care of himself is a good start since that’s what teenagers and young adults should be doing. I would get him driving lessons with an instructor (that way he’s not reliant on you- it’s something he can do ‘by himself’ to feel confident. Also your relationship sounds strained so teaching him might be a nightmare). It would also be good for him to get a part time job. Even though he might hate it, it will make him feel more productive once he gets used to it (it might take literal years). He also needs friends that aren’t wrapped up in transgender politics which is going to be more difficult. Even though he’s the one at fault, he probably perceives your relationship as so broken that he won’t listen to a word you say and you may need some sort of outside intervention of a family friend who can be “on his side.” (Even though you very much have his best interests at heart.)
If he spends more time on those aspects of a positive identity/sense of self then he will stop focusing on trans ideology so much. He might feel that those things are impossible (feeling like he needs to fix the “transphobia” issue in his life before becoming more functional or that his problems can be blamed on transphobia ex: “I can’t have mom teach me to drive bc she’s transphobic. I can’t work retail bc I will be misgendered and customers will use the wrong pronoun.”) It’s going to feel unfair because the economy is unfair to everyone but especially gen z and millennials right now. He’s going to hate it, but it’s better that he learns there than in Boston. (I learned all of these things in a big city all at once and it’s sooo much easier to take small steps than being on the verge of a mental breakdown for a year while figuring this stuff out).
If it’s possible that he’s gay, then he might benefit from having a gay counselor/therapist/mentor that’s not into TRA stuff.
Also I wanted to mention that I “ghosted” my parents while unable to drive. Uber is accessible now. I left home one day with nothing but my social security card, state ID, laptop, phone, and a couple changes of clothes. Lgbt groups do tell you what you need to know to get out of abusive households undetected, and even though you’re not abusive I bet that he’s reading those sites. It was awkward trying to get a copy of my birth certificate and back to a semi normal life again, but it’s very doable. Of course, paper trails get laid pretty quickly, but my parents still haven’t contacted me.
Leaving home when you have a homophobic parent or “transphobic” parent is heavily romanticized in some circles. I don’t regret it, but I think we put a more positive spin on it due to the hurt and trauma and impossibility of having a relationship with parents. It’s unfair to teenagers. If my parents weren’t also abusive on top of being homophobic there are definitely times that I would have begged them to take me back or contacted them to get me out of my own mess. There’s a sense of pride in saying “oh, I work 2-3 jobs and lived in a cockroach infested apartment, but I’m going to go to grad school and get out of this mess and I’m doing so much better than I was!” It sounds heroic on paper. In reality, I cried a lot. It’s a lot to go through and lgbt teenagers are completely unprepared for it- I definitely was.
It’s going to be a long process since he’s going to have to admit to being wrong about something so fundamental to his identity. I’m friends with some detransitioners, but really have no idea what they’re going through. I would read some of their work as well. He’s also going to have to confront that he has wronged you which is going to be hard as well.
Hopefully a lot of it is just talk/bluff and he won’t leave. Feel free to ask me questions about my experience if you would like. I’ll pm you any answers that are more personal or that I don’t feel comfortable answering on a forum!