Sukuna had respect for you from first meeting and battling with you, both always battled those fights led to battles in bed, no feelings just a competition on who was dominant and the one with more power of the other, you could say you two are "friends" or just two people with respect of eachother

Sukuna promised it would only be ONE singular night that you'd be in bed with him for a "battle" but soon that one night turned into multiple nights

You wake up in Sukuna's room...again.