They've been by your side since before you can remember. They were your first real responsibility. The first thing, other than your parents, that you loved unconditionally. No matter what horrible adolescent thing happened to you as you were growing up, coming home to that unconditional and unending love made all of the drama meaningless. Don't lie to yourself or anyone else, you let your dog lick you on your mouth because that's the way you show your love. No matter what happens in your life, no matter how many pets you have in the future, you will never forget your first dog.
It's an unbreakable bond. It's a never ending friendship. If you pet another dog you feel instantly guilty. If you come in contact with a cat anytime throughout the day you do whatever you have to do to cover up the scent so your best friend knows you're not cheating on them. You have probably taken over a thousand selfies with them and maybe two of them have come out acceptable because you're dog has no chill. Selfies are hard enough, forget about candids. You can try a million times but all your iPhone can come up with a blurry smudge running across the screen. But you still love that blurry smudge more than life itself.
You and your dog have watched each other grow older. Seeing a grey hair on your dog's face slowly breaks your heart. You have more memories with them than you're capable of telling. It seems like a lifetime of friendship but in reality it's probably been less than 10 years.
Somedays we walk right past our pets without paying any attention to them at all. Take a moment and stop to look at them, I guarantee they're staring right back at you. Isn't that amazing. Loyalty at it's purest form. You could ignore them forever and they would never stop staring at you. They love you unconditionally no matter what. Take some time to love them back.