You were either super dense, or acting dumb and pretending you haven't noticed Robin's obvious hints. It was probably the latter.

This man would run laps just to try to get you to swoon, but you never did. You were just so blissfully unaware of how your very presence caused a storm of emotions in him. He both hated it and loved it at the same time.

But, how to make it more obvious by watching the stars together? Hopefully you'd finally notice.

"So... just you, me, and the stars. Feels pretty more-than-friendly, if you know what I mean." Robin said as he subtly scooted towards you.