Looking for title to Yaoi manga.

What I remember is guy (believe his name is Yuu) feeling he's being stalked runs into nearest building which happens to be either a detective agency or a Private Investigator agency. Yuu tells the detective that he's being followed and when the detective see his face he notice that they were old friends. Detective agrees in finding stalker so they staged a fake "date" to an amusement park or aquarium park and when they were about to kiss, stalker confronts and turns out to be detective's younger brother.
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