So basically, matespritship is love. Like, what Karkat and Terezi had going.
A morail is close friend or a comrade, morails sorta keep each other in check. Look at Equis and Nepeta, Eridan and Feferi, Vriska and Terezi. They usually have somewhat complimentary personalities.
Those two are red (flushed and pale), they're "positive" relationships. Then you have negative relationships, black (and gray, technically).
There's the kismesis, which is a person you love to hate. That's Karkat hating on himself, hating on John, or Eridan hating on land dwellers in general - except that's unrequited because no one really - no, wait, Sollux and Eridan. What's NOT a kismesis is when you hate someone to the point that you actually seriously hate them and want to kill them (Karkat to Eridan after he kills Feferi and Kanaya). The point of kismesis is a rivalry.
And then the one you're wondering about is that auspitice s**t. They's complicated because it's a three-way relationship, with one person acting like a referee. The key point here is that for the most part, the person who is the third wheel is acting so with the understanding that this is not for their benefit. Kinda like matchmakers, kinda like referees, kinda like middlemen or messengers.
The deal with Kanaya is that she has a bit of a crush on Vriska - they're morails, and I think Kanaya was looking to go a bit redder. She's upset because Vriska has decided to chase after Tavros - something about his woobie and weak personality appeals to her. I think she's fascinated at how easily he can be manipulated or something. Kanaya becomes jealous once she realizes that Vriska is trying to create a redder/blacker relationship with Tavros. She doesn't really lash out at the boy (as far as I can remember) but she does take a bit of satisfaction in sawing off his legs for Equius.
At some point, Kanaya becomes fed up and gives up chasing after Vriska, as evidenced in one of the Alternia walkarounds - I think it's Past Karkat: Wake Up, where you can play as Vriska and then talk to Kanya as her.
So when Kanaya dies and comes back to life, she decks Vriska in the face because she thinks she's a dumb b***h now. And when Vriska saw how cool Kanpire was knocking Gamzee off the cliff, punching her, breaking Eridan's wand and then sawing him in half, Vriska was all heart heart heart she is
awesome.
Except, actually, I have no idea whether that happens before or after Vriska is confronted by Terezi, as per the current updates. I know the current scene is after Terezi is bitten, but.... Has Vriska been punched yet? Her lack of glasses would indicate so, since they were broken by Kanpire's punch. But then where's Kanpire?
ANYWAYS.