When you are in love, your brain secretes oxytocin, which in some studies is also known as the hormone of love. It is this that causes you the butterflies in your stomach every time you see your boyfriend, and the one that makes you feel so good.
With this in mind, at the University and Claremont they did an investigation in which they measured the chemicals released by the puppies when they were close to someone they show affection.
It turns out that they have an increase in this same hormone! What makes them feel love for their family. This means that when your puppy sees you, he feels the same as you do when you see the love of your life; although clear on a simpler level.
Your hairy little friend can not buy you chocolates or take you to the movies, but rest assured that all his feelings towards you are beautiful and sincere.