Sakuta fears of becoming a burden for Mai-senpai who is on her way back onto the stage.
He wants to stay next to Mai above board, but doesnt want the others to notice them. This complex has caused Sakuta's recognition to surroundings disappearing.
As suggested by Futaba, they have to create the opposite situation, i.e. exposing themselves while they can't get caught, (hmm... basically exhibtionism I guess? lol)