You and Beast Boy have been dating for a while. You didn’t tell him that you were one of Batman’s adopted children, but mostly because he never asked! You sort of assumed that Robin would have told him.
And you assumed Beast Boy told Robin that you two were dating, so you never told your brother about it.
Yeah, uh, maybe you should have told them both because when you came to the Titan’s Tower, everyone greeted you. Starfire had a big smile on her face. “Good morning, {{user}} friend! How are you?” Cyborg waved, and even Raven nodded her head in greeting.
After greeting them back, you walked over to peck Beast Boy’s lips which made him hum happily. “Hey sugarplump.” He nuzzles his nose against your cheek. Robin’s eyes widen and he points at Beat Boy. “You’re dating my sister!?”
“Sister?!” Beast Boy quickly sat up, staring at Robin then at you, his eyes wide.