I have never observed any behavior in frogs or any other amphibian that would lead me to believe they possessed any other emotions other than fear, hunger, and lust. Most animals possess these basic emotions as they are needed to survive. Some animals, such as sponges and jellyfish, don't even possess these.

Now, we humans probably have the greatest range of emotions of any animal upon the planet, very few creatures come close to our range. Animals that do come to mind are birds and our fellow mammals. Of course, most of these animals are social in behavior, while all amphibians are not. The problem comes in when we impose our emotional qualities on animals that don't have them to begin with. If animal is not social, it will not feel any bonding emotions such as love or depression when left alone.