The general rule is that Nobara is always the top alpha. Do you think there will be an exception? Like what if Yukino gets* cough* accidentally *cough* drunk or something. Sometimes people like Yukino who always try to control or hide their desire might just reach their limit.
Nice catch, Yukino didn't find it weird that the pillow was there so indeed they must be sleeping together (͡ ° ͜ʖ ͡ °), maybe even doing some hand holding, how lewd.