Here is the full list of all 8 Pet achievements.
You already made your decision.
I'll always love you for taking care of me.
Someone got a new pet.
You went to the vending machine, and you met someone.
You emptied the whole machine.
You went to the vending machine, but you didn't meet anyone.
You picked the wrong path. Maybe on purpose.
You left without going up to the vending machine.