Questions that nobody will answer!!!!!!

Is it possible true that the new age of things to do is to just cheat on each and as long as the other person does not know then it is really OK to do it.  I still do not understand how people can cheat, and if the main reason is that they do not like the person that they are with then they should just break up the relationship that they are in and just move to the next one.  Can somebody tell me why the necessity of cheating???