Didn't jasprosesprite and nepeta talk about how Dave and Karkat were dating? And I think Vriska and maybe even John said something about it too?

Jasprose referenced that Karkat was dating someone but that could have just been a cagey response to convince Nepeta that Karkat wasn’t available and that she should date them instead.

Vriska suspected that Dave and Karkat were involved in one quadrant or another, whether that be Flushed or Pale

And John asked Dave if he was gay, and he said no but that doesn’t mean he’s not something else.