All of Kuo's actions are because he is strange. He always acts without rhyme or reason, and seems to ignore social cues from everyone. Also, nothing there is forced. Kuo is pushy, but never forced Yukio to do anything. Yukio went along with it because he wants to make Kuo happy.
Personally I'm happy with either.
I mean, it would be super stupid if it was just 'hey she's my childhood friend that means she's the right choice!'. he has had a relationship with f-cup and it seems to have gone well, they both seemingly care(unless another equally stupid development happens...