Depth of feeling can easily be measure by the intensity of a person's listening habits.  When a person truly cares for another, they want to know what that person thinks, what is important to them, how they feel about any given subject or something as simple as how their day went.  I am not referring to polite listening, when you stare off into space or impatiently wait for a break in order to turn the conversation around to your own thoughts or needs.  I am referring to true listening, when you ask questions and really want to know how that person sees and feels life.  When you think about the answers and gain some understanding of where that person is coming from.  When you are interested in what life experiences brought them to their conclusions.
Have you ever watched the body language of the person you are talking to?  Do they appear impatient, give you the impression that they wish you would just finish what you are saying so that they can talk or go do something else?  Do they actually turn their head or sometimes even their whole body away from you?  Have they gone so far as to get up and walk away while you are talking to them?  If so, you can bet that they are not interested in you as a person, only whatever needs you may fulfill in their lives at the moment or they feel that it is to their advantage to tolerate you but they are not looking for a deep and giving relationship.
Do you remember when you first fell in love with someone, you hung on every word, analyzing everything they had to say in order to better know and understand that person?  Your desire to learn how they thought and felt about things was genuine and intense.  But as time goes by you reach the conclusion that you know everything that is worth knowing about them or you have decided that you know enough to fulfill your own needs so you lose interest, you stop listening.
People change every day, you never know everything there is to know about someone.  By listening to others, we learn about ourselves, we ask ourselves the questions that allow us to grow, as our feelings for those around us grows.  We lose our selfish and self-centeredness and learn to truly give of ourselves.  We begin to realize that the important things in life are in the minds and hearts of those we love and that these things are all that we can take with us when we go.  It is also the only thing of value that we can leave to those we love, the part of ourselves that we shared while we were here.