If we analyze the chapters, it seems that none of Hikari's friends knew her crush was Aya's ex, that Aya didn't know he was Hikari's crush, that he didn't know Aya was Hikari's friend, that he didn't even hint at who he was actually interested in and that Hikari never told her friends his full name to begin with. The whole story is from her perspective as an unreliable narrator. She also only started crushing on him much later...
...Hang on, does that mean Hikari is technically the one who's wrecking another girl's relationship then?