I just read your description of Kane, and thought you might like some input from the owner of Filas.
For a Fila, being an "only dog" not only isn't necessary, it's not good. Filas - in contrast to so many of the Mastiffs - are remarkably affable with other dogs and are happiest in a home with another dog. They are truly family oriented creatures. They tend to be obsessive, and having another dog - or two or more, lol - in the family definitely makes life much easier for all . . . and it's so amazing and enjoyable to watch how gentle these great creatures are with smaller, weaker creatures.
They are also dogs who NEED to be with their people. These are not dogs who can live in the yard, or be kenneled without a significant amount of inside time with the family.
I hope Kane finds a wonderful home full of love and laughter. The Brazilians have an old, old saying, "faithful as a Fila," and it is demonstrably true.