I always love it when I'm like, "I'm a lesbian", and people are like, "Oh, but let's deconstruct that!". I think the idea of escaping labels in Homestuck is funny because it ironically has its limitations. Dirk rejects the use of the word 'gay' because he's the last man in the world and there's no more culture so what do words mean. But functionally, he's still 'a man who loves men and seems to not be interested in women'. No catharsis comes from trying to force himself to act differently during Trickster Mode. So whether you label it or not, the label still paradoxically survives its interrogation and retains meaning.

Dirk is gay.

Kanaya is a lesbian. I headcanon Rose as lesbian, too, but there is no confirmation of this, and who knows what they have planned in postcanon.

Oh, and a good rule of thumb: Most people in the world are straight or bi, and fandom demographics will usually reflect this. So characters will almost always be treated as functionally bisexual by a fandom since they want to see themselves in the shimmering mirror of the story, even if said characters are lesbian or gay.