If you have a friend or acquaintance whose spouse you've observed being unfaithful, you could be left in a moral conundrum. Your knee-jerk reaction is to tell your friend immediately about the infidelity, but taking into consideration the context, viability and nature of your friend's spousal relationship could stop you from making a poor decision. If you must let someone know their spouse or partner is cheating, doing so with tact and offering support can help your friend through an emotionally draining and confusing time.
Decide whether or not you want to tell your friend or acquaintance about the adulterous behavior. Consider whether you have enough reason to say anything and how your news will be received. Take into consideration the boundaries of the relationship; some relationships maintain a certain degree of openness. What you perceive as "cheating" may be acceptable within your friend's boundaries and type of relationship.
Reverse the roles and consider whether or not you'd like to know if you were in your friend's shoes, suggests psychotherapist Cyndi Sarnoff-Ross of DailyStrength.org. You may find that, when put in the same position, you wouldn't want to know about a cheating partner. While your gut reaction would be to tell immediately, think about the repercussions that your accusations could have on the couple's relationship and future together.
Gather all of the evidence possible to accuse the spouse of indisputably cheating. Never trust the rumor mill, online social networking sites or a one-time sighting taken out of context, warns ImprovingYourWold.com. Do the legwork for your friend and wait until you see it with your own eyes so you can make a sure accusation that you can back up with the truth. Telling your friend merely that you heard the partner was cheating can be hurtful and damage your own relationship.
Confront the cheater first. Give them the chance to come clean. This type of news should be discussed privately within the marriage. Call and say that you've observed the cheating, and plan on telling your friend at the end of the week. This gives them the opportunity to confess and work it out together before you have to make an accusation as a third party.
Contact your friend if the cheater refuses to come clean. Choose a neutral time and place to give the news, as it will likely be upsetting. Avoid public places or a cramped schedule because your friend may need support and a shoulder to cry on when you reveal what you know about the infidelity. Your friend may not take the news well and may even become angry at you for making the accusation. Once you've said what you know, though, the information is out of your hands, and your friend can choose what to do about the relationship going forward.