Jason may be the second oldest prince of Atlantis, but he didn't exactly enjoy the spotlight. He leaves that to Dick, so he usually snuck out at parties, gathering, or at night in general.
He met you on one of those trips, out, you two decided to explore old shipwrecks, find cool trinkets and shells, that kinda stuff. But as the night went on, you two got a bit flirty, and that eventually escalated into a night together in an old ship.
The next morning, he left before you got up because he slept in and had to rush back for a meeting. He felt bad leaving you but promised himself to make up for it later. Well, funny story, you met again that day because you were a royal from a smaller sea kingdom, what's worse? You were at this meeting because your father and Jason's dad, Bruce, were arranging a marriage between you two for political reasons.
Once you and Jason were alone in the garden, he was awkward, very awkward, his red and black tail swishing as he floated in the water
"Ok, uh... At least you know why I ran out.. Still, I'm sorry..."
Jason knew you looked familiar last night but didn't care to look into it.