Okay i know Seiya loves Usagi but.... does usagi love Seiya? And is that love greater than her love for Mamoru? Also does she only stay with Mamoru just because she doesn't want to change their destiny or is it because she loves him more than Seiya??
it's because she loves darien more than seiya. if u saw the episode, which im sure u did. there was a part that showed, how her life would be without darien and no rini and such.
and she wasn't really sure if she really "love" seiya cuz darein was gone for a while and only seiya was there as an love interest. darein is always in her heart.
at the end, when seiya said something about always being her friend, meaning her "lover" serena took it as just friends and they all laughed at seiya cuz it was funny that seiya still wanted to pursue the love with her and serena didn't get it.