Ive felt that, if you look closely, you can see you get a small high from being nice. When you are nice, more like kind, to someone, it makes you feel good.
Ive been thinking that love and kindness and compassion is kinda the same thing. Like romantic love is the comes from the same place as compassion but with some added attraction. And the idea that we should be loving and kind to our partners, even when they are mean, that idea is present so deep inside us, that it keeps us kind even when we would be a jerk in other situations.
Maybe we lack the idea that we should be kind and nice to everyone, if we were raised believing in that idea, maybe we would all be a lot averse to acting like a jerk. It maybe due to the climate of fear in which we raise children, they are thought to think of strangers as evil and not kind and no wonder we dont hold the concept that we should be kind to others no matter what. But we easily hold that concept about our loved ones.