He is not the only guy that will ever want to be with you. But for another guy to enter your orbit you have to be willing to make a space.
There's another girl he's in contact with, and even though I didn't really say much about her, he somehow figured out that him seeing her made me uncomfortable, and voluntarily told me that he'd keep her in the friend zone until I figured it out. So he made a concession there, but I can't figure out why he won't make one here. Maybe I'm asking for too much?
I can guess.
Maybe I'm cynical, maybe I guess wrong.
But maybe he tossed you one he could really care less about? Mainly so later
he can point to it and hold it over your head as example of how "understanding" he's been for you before and how "unreasonable and selfish" you are being now. Using it like tool to get his way later?
You did not ask for him to make concession with the friendzone woman. He did it "voluntarily." Keep that in mind. People who do things voluntarily as a gift don't draw attention to it or come round later with "now you owe me" attitudes.