I bring canon proof (ie. lots of screenshots) for (and all I needed was ONE episode - Episode 17):
WARNING: SPOILERS, SPOILERS FOR TIMESKIP
Why Simon/Rossiu is Completely Canon
#0: When We Were Two Little Boys:
[icon by flauta_de_pollo]
Simon: LOOK LOOK ROSSIU: I'll be your Peter Parker if You'll be My Mary Jane!
WATCH OUT VIRAL, ROSSIU DOESN'T LIKE PERSISTENT GUYS SO NEAR SIMON:
ROSSIU: PUT AN END TO THAT FLIRTING RIGHT AWAY.
Rossiu: You have trespassed on MY - I mean, STATE property -"
Rossiu: "AND YOU WILL BE PUNISHED."
#2: ROSSIU: I'LL BE WATCHING YOU / GIVING OBSSEIVE STALKERS A BAD NAME:
This is right after Nia accepts Simon's proposal:
Rossiu's SOMEONE IS HOMING IN ON MY SIMON SENSE IS WORKING REALLY WELL:
Rossiu: Yes. Your @$$ is mine, you're not promising it to anybody else.
#3: Princesses Getting In the Way
Rossiu: Yes, and she'll be showing up in short order.
Rossiu: RIGHT ON TIME.
PLEASE BE NOTING ROSSIU'S DRAMATIC CHANGE IN EXPRESSION.
(the eyebrows say it all!)
#4: AND FINALLY, WHY THIS EPISODE IS NAMED WHAT IT WAS:
Rossiu subtext: I DON'T WANT TO LOSE YOU LIKE YOU LOST KAMINA
SIMON IS LESS THAN RECEPTIVE:
THAT'S WHY THIS EPISODE IS CALLED:
Because Stupid Simon is Stupid.