There are so many reasons why a person will stop loving his or her partner.

1. he or she might have fallen in love with another person.
   2)if one feel cheated or caught the other in the act. "Betrayed"
2. if you feel unappreciated .
3. if you feel unattended to,or uncared for and you are being cared for by another.
   5)distance could also be a good reason.
   " Out of sight is out of mind"
   6)if both parties fight and quarel always..love fades away...