If Love is painful you may be doing it wrong. Maybe you should roll over or trade your black boyfriend for a white guy. If you speak of the heartfelt pain of love lost, which is very real, I think it's because of what pain is. Pain is our bodies reaction to being hurt. We can't be expected to monitor every portion of our bodies thru visual inspection every second of every day so nature provides us an alert system to make us aware of where to look. The hurt love causes is nature's way of contending with a missing ingredient that makes us whole. There is a hole in my heart that can only be filled by you is symbolic in words but the hole will literally cause pain when the body senses something missing. We are made aware of the positioning of the pain but it remains invisible to our eyes and without some physical reference our minds can't grasp the remedy to seek. We simply know, in the past, the hurt was not there and we try to retrace our steps to find that missing piece with all the conflicting feelings of cause and effect. Somewhere in the past is both the cause of and remedy for the pain we feel. Do we take the remedy of returning to a place we were for a moment without pain or endure the pain while seeking a more long lasting remedy.
It's true if we keep our hearts pure and without spaces to be filled we will never know the pain of those spaces being empty but our hearts would be no more than a pump you could buy at the right hardware store. The more we let into our hearts the more chance we have to allow the pain to exist.