Next day? Though from what is implied in the story so far, the relationship between ouji and Nagare isn't that close. And ouji-kun so far had no reason to hide from fangirls. So maybe, he wanted to approach nagare, in pretext of protecting her from fangirls? After all, Nagare goes from the windows, so there is bound to be someone in Ouji-kun Fangirl who saw them colliding.