Are you saying that cheating on someone is due to a fault of the person you are cheating on? Well, depending on the society you live in, and the viewpoint on monogamous or polygamous relationships, I doubt it is of any fault of theirs. Depending on your morals, it is your conscious decision to cheat on someone.
As I've learned throughout my life, taking responsibility comes hard for people (I used to blame my parents for my problems after they divorced and instead of going forward, I used to wallow in self pity). However, in this case, if you cheat on your partner, I think it is your mistake. If you have a problem with your partner, bring it up with them. Transparency, bluntness/being straightforward may hurt, but it lessens the chance of betrayal and emotional distress. Think about the repercussions, then act accordingly.