Yoo in the lore do Kan know what Nita do to Yuna and with who Yuna have s** for the first time?.
Personally I firstly think it's was with Kan to be able to continued live the apartment, but then I remember that she don't need to pay because she haven't fail in the school or something like that, or her first time was with Nita. Anyway the Yosuke lore is more entertaining that Yuna.