Cats don't always express emotions the way people do. They certainly feel emotions, but they have their own ways of letting us know how they're feeling. Affection is pretty obvious, but they get jealous and can be in bad moods too - which a good scratch behind the ears can turn right around.
There's at least one cat in the world showing an emotion that's just not there, though. It's as adorable as anything you're likely to see in your life, and that's why it's breaking the Internet.