I just thought about a thing,
While all the trolls are singing “Fixer Upper” (and shipping Kristanna before it was cool), Kristoff screams “SHE’S ENGAGED TO SOMEONE ELSE, OKAY?”
He didn’t say “GUYS, STOP FANGIRLING, SHE’S NOT MY GIRLFRIEND!”. He said that she was engaged to another man.
He was like “Guys, please, don’t make me feel even worse. She’s engaged to a prince and she’s a princess, she would never marry a man like me. So please, stop make me feel like an idiot and save her. This is all I want.”
I think Kristoff loved her, and even if he knew he couldn’t be her fiancé, he wanted to protect her and try to do as much as possible to save her.
Oh Kristoff, you little, handsome, shy, adorable puppy.