It's hard, I mean I know I fear that "losing everything" feeling, feeling selfish and so on but ultimately, at the end of the day, you have to do what is best for YOU and remaining in this shadow of a life is going to kill you.
Ultimately, while it's less than ideal to have such little support from your other half, it's something a lot of trans people have to go through to become their true selves. It SUCKS and it's not fair, but some people put far too much stock in gender when it comes to their partners and it's unfair to force them to stay if they're uncomfortable.
on the other hand, it's pretty unfair I think for a partner to force you to stay "in the closet" when they should be able to see the harm it's doing.
At the end of the day, this isn't about THEM, it's about YOU and you have to put yourself first.
Maybe he'll adapt, maybe he won't, but remaining as you are doesn't sound like it's at all tolerable and as time wears on it'll just cause resentment between you anyway.
I really wish it was possible to wave a magic wand and make everything good and right but sadly life just isn't like that.
I'm very fortunate I suppose in that my partner is bi just like I am, had he been straight he'd be running a mile i'm sure. And even being bi he's uncertain about all this as he's never been intimate with a guy and it's a big change.
I still worry it'll be "too much" and he won't be able to do it.
I can already sense him tensing up when I mention changes I look forward to, and he's started growing his beard out which is totally a power move of "masculine machoness" lol. Cismen are so ridiculous.
Seriously, I get the real feeling he thinks me transitioning is somehow going to detract from his own masculinity, like, if I have better facial hair or chest hair it somehow makes him "less of a man" and i'm like "honey, look at it this way, you'll always have a bigger dick!" which seemed to cheer him up a bit.
Anyway i'm rambling.
Point is, it's a huge change in the relationship and most couples sadly don't weather that storm. But I remind you, your mental health is MORE IMPORTANT.
and it's not your fault. Don't feel guilty, don't feel selfish, don't ever let yourself feel like you're a burden. That's depression being a jerk and lying to you. I know that's hard, to tell yourself it's okay to take the plunge and throw everything into chaos but hey, sometimes you need to strip away dead wood to grow. Great forests grow from scorched ground.
You can do this. You've survived this long, you're STRONG. You can do this.
And when you stumble, we'll all be here to help okay?