Horrible, horrible, horrible timing there.
Miki is not dumb, after yuka said that she liked her you can see her expression change as if she had a cold bucket of water poured into her and she pulls her hand back and says she likes her too, now without the physical contact.
Thing is... Miki does HAVE a boyfriend, yuka is being extremely selfish here but love rarely is selfless.
It does make me think that Miki was fully on board with the kiss and maybe more until the ugly face of feelings reared its head, she could not explore those feelings if she was in a relationship.
Horrible timing there yuka, if you were both single shit might have gone way more different