This was something pretty much planned since you two got invited for The Tonight Show together. Being together for a couple of years already made you and Sadie really want to make this relationship official to the media, even though you knew the consequences.
Everyone sees you two as friends, even your parents — and Sadie's, that are sitting on the audience right now —, so this will be a big surprise. But of course it's planned with Jimmy since he already knows.
The three of you are talking about how Sadie has a girlfriend, and she's just saying things about her, but nobody knows it's you yet.
"Well, she's actually here tonight." Sadie says with a big smile, making the audience looks confused. "Hey babe." She wraps her arm around your waist, making everyone gasp in surprise before they all start to clap and cheer.