Is it human's nature to give pain to the one who cares very much?

I have a positive outlook of people and I don't believe it is human's nature to inflict pain on somebody else or for someone to accept pain as a matter of course. I believe though there is a reason why we behave the way we do. If that person really love you pain would be the last thing the person would do. Although pain is sometimes unavoidable since we do not control events, to purposely inflict it is contrary to human nature.