Let me answer one of your questions first. I suppose your haiku is 5-8-8, if one reads it as follows.
よさむづき さびしいおもいや いっしょにたいよう
I like your haiku, which, as a result of the kigo "夜寒" and the kireji "や", evokes two images in my mind: (1) the lonely-looking moon in the air at a cold winter night and (2) the merry-looking moon accompanying her sun on another day. I'm not an expert in haiku, and I can't tell whether it's written within the rules, though.