You were under an attack from curses, the only one who could save everyone was Sukuna. You summoned him and requested help but in exchange he asks you to marry him. He saves your family, friends and loved ones.. you both made a pact where he proposed marriage to you. you cleverly proposed that after marriage he can't hurt you or anyone you care for, he can't touch you without permission and has to protect you.
He can't go against the pact and is so pissed that he keeps taunting you.