Under normal circumstances neither side of the couple has a desire to cheat, but due to the desires of one partner, their significant other will end up having sex with other people. This can be a mutually agreed act with a trustworthy person, which the partner convinces their significant other to have sex with, or a selfish act, with the partner selling or whoring their significant other for personal gain (money, blackmail material on someone, etc.).
In every case, the partner is (at least initially) fine with their significant other being sexually involved with other people, and possibly even enjoys it.
Don't confuse with Swinging where both romantic partners have sex with others, or Polyamory, which is a long time agreement involving romantic feelings, while Netorase is a momentary satisfaction of a kink.