My friend only calls when she wants something. I tell myself that helping her is part of the give-and-take of friendship, and that she will be there for me eventually, but she never is. What should I do? —Robert, Boston

We have all been guilty of using a friend selfishly, so before bailing on your pal, tell her calmly how you feel. Here’s hoping she takes your reasonable message to heart.

—Adapted from ‘The Ethicist’ in the New York Times Magazine