Human relationship is a complex interplay of emotions. It is very difficult to predict when would a particular relationship turn sour. It could be due to mistakes committed by both but many times you are not the offender. In spite of your best efforts you are unable to heal the relationship. Some people are just not capable of love. The best thing you can do is to forgive , let go any anger you might have gathered all along , wish well and move on. It is just a matter of time that somebody would fill up the space created within your heart . That somebody could be your soul mate just waiting for the chance.