Cheating is a "cowardly act" perpetrated by people who seek to hold onto all that is good in their primary relationship while addressing other needs/wants on the side.
A honest person raises issues of concern they have with their mate. If they are unable to come to an agreement then a decision must be made as to whether or not they should continue with the relationship. There is always a risk of throwing away "a known something" that is 75-80% good for an "unknown" future opportunity. It takes courage to walk away from a "known" to pursue an "unknown"
The politically correct thing to say is "It's never ok to cheat". However in reality I know (people make up their own "rules") in life.
Cheaters always find a way to "justify" their actions!