Yeah, I can relate. One reason my ex was attracted to me in the first place, apparently, was my unconventional appearance. He liked my no-nonsense presentation, didn't mind the androgyny (unless I was actively binding or something), and knew that I was trans in the first year we were together.
We were together nearly twenty years before I started transition. It took him less than three months to decide to break up with me. And that's a man who already knew about me and was okay with my gender identity and "cross dressing." As long as I never actually DID anything about it, he rarely had a problem with it. And he was the biggest reason I never transitioned. There were other factors, but my relationship was the most important. Twice I got to the "I can't take this anymore" stage, and twice I managed to bury my true self or compartmentalize my life enough to go on as I was. The third time, I just couldn't do it anymore.
Sometimes I wish I hadn't been so stubborn and so scared.
Now he's going the other way, looking for a feminine woman who is 5' 2". Once burned...
All relationships have their own dynamic, but your situation sounds problematic already. I wouldn't hold out too much hope that he'll accept you, but you can't really move forward (not honestly, anyway) until you tell him. For you, perhaps, it's even scarier because you seem pretty sure that he won't stay with you. But at some point you'll have to punch through the love and the fear, and run the risk. Or maybe what you're really doing now is reconciling yourself to the near-certainty that he will want to break up.
But I guess you already know all of this, yes?