When do you "come out" to someone who's into you?

Tij🌸 • Creative Writing & Quantum Mechanics Major. Which is fancy for big nerd.
Let's say, hypothetically, you're agender and pansexual and this guy you met at a poetry slams once upon a time digs you. & he's cute and you've been talking lots about the universe and capitalism and who you want to be and the stars in comparison to your eyes, and he says. Let's go on a date. 
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You say, alright sure. And on Twitter, you see he posted about you (she gets me!!😍) which is cute and you're not offended by the pronoun use... But you ARE agender and you DO prefer they/them pronouns...
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So, theoretically, when should you bring that up? Should you ever bring it up?
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 It's not like I'm (er *you're*) offended or angry or even oncomfortable... Ok maybe you're a bit uncomfortable... That's not your pronouns. It feels like you're hiding who you are from him. Feels like you're lying...
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Help?