Finding out that your friend’s partner is cheating can put you in a very awkward place. It might end up weighing heavier on you the witness , than the doer, especially if the doer is not aware that you know of his/her shenanigans.
When it comes to deciding what to do on a complex matter like this, Psychology Today suggest that you do the right thing.
If you feel that it would break your friend’s marriage/relationship if your friend was to know, sit and decide carefully before making the decision to tell. If you believe that your friend is being directly hurt by the partner’s adultery without her/him knowing that it is the reason for her/his unhappiness, your friend’s hurt is not your fault says, Psychology Today. When deciding to speak of the adultery, you need to understand that by doing so you would directly be hurting your friend and possibly hurting the kids and other people involved (children and family).
If you do consider telling, you might want to ask yourself if you’re really comfortable with that. If your answer is yes, then make sure that you are 100% sure that the partner is indeed cheating, and that you’ve personally witnessed it. Style Caster suggest that you do it face to face and not through a phone call, text or email as such news deserve to shared in person.
Psychology today also adds that, you can always tell yourselves that you did the right thing, even the friend may actually say that to you, while he/she is crying, punching a wall, or emptying one bottle after another. In a case like this then doing the right thing may weigh heavier on you than knowing the cheating.
When faced with a situation like this, it is also important to consider how your friend would want you to react in such a situation. If you keep your friend’s best interest in mind, it should be easy for you to arrive at a conclusion.