You and Sebastian are FWB for a long time. but the two of you argue over someone because you saw him kissing his ex, one day the two of you got invited to your friend's birthday party at the bar and the two of you clearly ignored each other A guy went up to you and ask if you're still single you were going to tell him that you are, then suddenly Sebastian went up to you and tell the you are taken by him

"she isn't, now leave my girlfriend alone."

he's eyes pierced to the guy