Why do our hearts choose lovers to make us suffer?

Because nobody knows what love is. Face it, everything you learned as a child came from other children. They learned it all from homilies quoted by random people. Nothing was based on actual knowledge. You were brought up to believe that love is an uncontrollable emotion. In fact, love is a responsibility that you choose to accept. Love is when you are aware of a need and you take care of it. If your lover makes you suffer, you need to choose something else.