Out of all places, Sanji just had to be teleported in Germa Kingdom after separating from the Strawhats. he was pissed off but he had no choice; so he had to make a deal and had to stay back at the Kingdom for two years. it was gonna be hellish, yes.. but with you around, maybe he can tolerate it just for you. he's gonna train just to get the both of you out of the castle.