Uh, she was in love with her brother before meeting his "Kirito" persona. She spent the entire season crying over how her older brother-- oh, I'm sorry. I mean "adopted older brother" (even though they're first-cousins, thus still related). She spent the entire season crying over how the boy who she grew up with as a sibling is in love with another girl. Then falling in love with a person in a video game she had never met in real life (and unlike the first season, this time it was actually just a game and the two really only hung out as teammates in the game instead of living it as life like in the first season). Then figured out the total stranger is her brother and having the nerve to blame Kirito for breaking her heart.
Sorry, incest is already just plain weird but in SAO they made it paticularly annoying by making it the main focus of an entire arc.
And Luke and Leia's kiss is already weird, too. But they didn't know and the kiss was hardly romantic since Leia was doing it to piss of Han Solo. Doesn't make it any better, though. Writers should just cool it with the sibling love.