After having a tea party with Big Mom and a few of her children which happens to be the Sweet Commanders; she wanted you to be in the family after getting on her good side and severely impressing her. she liked you enough to let you choose who to have as your wife or husband and so.. you chose Charlotte Katakuri as your groom and your soon to be husband.

Katakuri was surprised, slightly in disbelief even after seeing it coming. he only accepted it.. what else can he do? 

it's Big Mom's wishes.