As someone who was/is homeless, and has been around many with animals, there is no love more powerful than that type of love. You can have that love for an animal, a child/baby, or an adult, but it's extremely rare for most people if not impossible.

They're your only true friend, the person who's always there for you, the one who will hold you at night, the one that cares about how you feel, the one that needs you just as much as you need them, the one that warns you of danger as you do for them, the one who will never steal from you, and the one that will always be with you and never hurt you.
You can be fully yourself and honest with them, and nobody else.

I've seen someone jump off a train moving 20-30mph and smash their shit up after their dog got spooked by a bang and jumped off right as the train was starting to move.
The bond they have is the bond that if broken shatters you and likely compels you to murder whoever broke it.