When you realize Father's one true wish was to have a son... A family... I'm literally falling apart guys

This explains why Yato loves humanity and never killed people for pleasure, but he only did it to make Father happy. Also why Father is so desperate to keep Yato by his side even if the latter keeps betraying him.

Now I can't stop thinking about Father being completely alone and desperate, then all of a sudden what he had always longed for appears in front of him: a son. He may think he wants to kill humanity, but deep down his REAL wish is what created Yato.