Looking at the pleasure centers of the dogs’ brains, the researchers found that nearly all the dogs responded to “Who’s a good boy?! You are!” (or whatever they actually said) with at least as much pleasure as when they got a Hebrew National. A fifth of the dogs actually preferred praise to food.

Berns concluded that dogs derive as much pleasure from love as from food.

As a somewhat obsessed dog guy, I’m the first to concede that a central tenet of doggie philosophy is to reject the whole love-vs.-food paradigm as a false choice. Dogs are committed to the idea that there is no such thing as too much of a good thing. But as almost anyone who has come home to their dog after an extended absence will tell you, dogs don’t go bonkers for missing loved ones solely because they think there’s a meal in it for them.

And yet, there are people who argue almost precisely that. There’s what I would call the dumb version and the smart version of that particular school of thought. The dumb version, as the label suggests, is dumb. It can be found in people who say things like, “Dogs just lick you for the salt,” or, “It’s just an animal; you shouldn’t care about its feelings.”

The smart version has more merit. Evolutionary psychologists and other scientists label dogs “social parasites” or, in the words of some, “con artists.” They claim that dogs evolved from wolves to exploit our weakness for cuteness. They also note that dogs evolved an ability found almost nowhere else in the animal world: to read human body language and expressions.

Indeed, Berns found evidence of this in his MRI studies.

Dogs have evolved as the most successful species on the planet at reading and exploiting humans. Parasites do not kill the host. Really successful parasites enable the host to survive better than the competition.
Win-win

What you've described is a mutualistic symbiotic relationship. Parasites have an exclusively negative relationship with their host.

Dogs have evolved as the most successful species on the planet at reading and exploiting humans. Parasites do not kill the host. Really successful parasites enable the host to survive better than the competition.
Win-win