At the beginning of season 2:
Julie Plec: Okay, who wants to be Bonnie’s love interest?
Nearly every male raises there hand
Julie Plec: Hmmm…okay I will split all of you up among Elena and Caroline, Oh! Steven I see you didn’t raise your hand so Jeremy will be with Bonnie this season.
At the beginning of season 3
Julie Plec: Who wants to be a love interest for Bonnie this season? And Welcome Joseph Morgan to our cast.
Once again, nearly everyone raises their hand.
Julie Plec: Okay then. I will divide you all between Caroline and Elena. Steven, you raised your hand? Well, you will cheat on Bonnie this season with your ex then disappear for half a season, how’s that?
At the beginning of season 4:
Julie Plec: Welcome back once again everyone! Love interests for Bonnie? Any takers?
Nearly everyone raises their hands.
Julie Plec: Michael? You will spend all your time with Caroline then Klaus will run you out of town and will continue to obsesses harder on Caroline. Steven, Jeremy will die mid-season, as will Kol, Nate. Ian, we want to pretend that Bamon has a chance but really we will go with Delena, Paul we want to rekindle the Stefonnie friendship for a full minute then go back to you two never having any scenes, Joseph, Klaus will threaten Bonnie in the first ep and never having anything else to do with her and Kat, sorry dear but we’re gonna kill off Bonnie. It’s been a fun ride kid, good luck!
Seeing as nearly every male cast member has expressed love for Kat/Bonnie and wanting their character to be with Bonnie, this is just what I imagine happens in the writers room.