I agree with WW. Unless there is a physical ailment or injury, it is usually indicative of some other problem.
I will not make a moral judgement on the merits of cheating except to say that if the relationship is a good one then cheating is a critical weakness in the partner that does so. If the relationship is poor, then both should address it!

__________________
Lots of people talk and few of them know, soul of a woman was created below

I can't get through to her 'cause it doesn't permit
But I'm gonna give her everything I've got to give.

I hear your sweet voice calling
out my name
As I stare from a six foot cell
And from beyond I heard the words
Deceptively Yours