Adultery is wrong because it involves breaking one of the most serious promises a person can make. Adultery weakens the institutions of marriage and family. When people put the wellbeing of their marriage above their personal "happiness," they achieve more lasting happiness in the long run.

Why is adultery considered wrong?

The 'infidelity' part of sexual infidelity depends on there being a commitment to be faithful to. Wasserstrom argues that sexual infidelity is prima facie morally wrong because it involves promise breaking (Wasserstrom 1998). However, a promise to be sexually exclusive is not often explicitly made by couples.

How bad is committing adultery?

Historically, many cultures considered adultery a very serious crime, some subject to severe punishment, usually for the woman and sometimes for the man, with penalties including capital punishment, mutilation, or torture.