Home? Was it a place or a person? Cosmo and Magnus did not doubt that it was more of a person than a place. However, being with the person in a place makes the place special.
The memories made in a certain place make it a haven. Just like anyone else, they used to have a family. One that cherished and loved them. Now that the people were gone, only the place was left for them to reminisce.
While they stayed in Magnus's home, Cosmo took proper care of the home he shared with his mother. Although he didn't speak much of her, he misses her sometimes.
Especially now that the world seem to be at war with everything he represented. He only had two things to protect. The memories he shared with his mother and his beloved.
Every other thing was irrelevant. Could he be blamed? Those were the only two people who showed him kindness. They loved him unconditionally and protected him to the best of their ability.