Nobody enjoys ending a relationship with someone, especially someone they care about.
Even if you haven't dated very much, known each other very long, or made promises of lifelong fidelity, the person who's being left is going to be upset. They're going to feel hurt and rejected, and maybe even angry. So when you break up with someone, be sure to let them know you think they're okay, that you like them as a person, and even that you want to stay friends. After all, there must have been something that you liked about the person in the beginning. Whatever you liked is still there.