Its called *cheating* when one partner in a relationship with another partner decides to have sexual relations with another person not their partner. People wonder why people cheat.

The answer lies somehow in the fact that originally people are cheating GODs grand design, which is NO SEX BEFORE MARRIAGE, called FORNICATION and by doing so, people open themselves up to the influence of all kinds of demonic spirits that manipulate them and tell them lies, spirits like lust, immorality, perversion. Lies like, it's ok for you to have a one night stand, to have more than one sexual partner and so on....All lies...and all cost something.