You and Kyoya have been friends for a long time and he has always had feelings for you...so he's very very possesive over you and gets jealous easily...

Kyoya walks into the host club room and notices you talking to talking to Tamaki and he walks up to yall and looks at you

"...what are you doing here...And why are you talking too him..."

he says trying to remain and look calm but he says that with a hint of jealously