Haha no sh!t 
Sure they can. Say for example if you have the other partner around for emotional support only but dont really love him, and if someone better comes along then its only a matter of finding a trivial reason (like an argument and a week long silence) to call it off with the other partner and then run away to the other better option. No point of trying to make things up with the other partner if you didn’t really have any feelings for him to begin with. Telling him that its over is optional too and not really required. Just wait for him to find out a couple months later and watch his heart shatter, should teach him a good lesson too.
