Adultery is defined as voluntary sexual intercourse between a married person and someone who is not their spouse. It is considered to be so wrong because it is the ultimate betrayal of a covenant or promise that two people make to each other when they get married. They promise to love each other and to be faithful to each other, giving themselves in the intimacy of a sexual relationship to only their spouse. When this promise is broken it has serious implications, not only physically and emotionally, but also spiritually, as every sexual relationship is also a spiritual relationship.
Sexual loyalty, which is synonymous with marital fidelity, is a promise that is typically considered to be the most serious and fundamental vow we take when we enter into a marriage. That’s why breaking that oath is considered to be so morally wrong, because the trust between a husband and wife is essential to the healthy functioning of their relationship. Some people may find sexual fidelity to be the most difficult part of being married, especially if their lives are marked by other examples of similar relationship problems – whether that be a parent’s demonstrated infidelity or have been cheated on previously.