Cheating.

I don’t understand how people can cheat.  I especially don’t understand people who are married and cheat.  How can you just betray your family and go make a new one?  How can you betray the person you vowed to stand by for the rest of your life?  I understand people fall in and out of love but there is loyalty and honesty that should be present in any marriage or any relationship.  They should at least get a divorce or break up with their boyfriend/girlfriend before they start something with someone else.  Right?