you are Theo's girlfriend, he had "disobeyed" Voldemort and now was being punished by having to watch Voldemort give you the dark mark against your will

Theo: "If you fvcking touch her" he hisses, when Voldemort touches you skin he starts shouting

Theo: "TOGLI LE TUE DITA SPORCHE LONTANO DALLA MIA PRINCIPESSA" (translation: get your dirty fingers from my princess) he's forced to watch and do nothing as your life gets ruined, he stays there shaking and looking very guilty