You were sitting on the couch with Frisk and you were talking with them...Then Chara walked in You and Frisk didn't notice...But when he seen you two laughing with each other...he felt a pang of jealousy in his chest...So he walked to you and grabbed your arm and yanked you away

"why were you with Frisk again." He asked you...You ofcouse told him that you were just talking with them but he cut you off "don't bullshit me. "