Answer: The prairie vole is an animal model of romantic and familial attachment and love.
Most animals in the wild do not form tight extra-familial bonds as humans do in (such as marriage). The prairie vole is an exception. Male - female vole pairs during the mating season often form lifelong bonds, displaying affectionate behavior such as grooming, cooperative nesting, and shared offspring raising responsibilities.
Males will remain socially attached to their female vole mate for life. If the female dies before the male, he will generally not seek a new mate pair.
This paired mating behavior is driven in part by the neurohormone oxytocin. In prairie voles, the receptor for oxytocin (OXTR) is densely expressed in the reward related structures, which reinforces participation of these social behaviors. Delivering an oxytocin antagonist, which will block the action of oxytocin during pair bonding, can prevent the prairie voles from forming these relationships.
Conveniently, there is an taxonomically related animal that does not show dedicated pair bonding, called the montane vole. These voles are often used in behavioral experiments as a control group.
Only a handful of species, about 5%, are socially monogamous. Prairie voles are best known for practicing lifelong social monogamy.