This isn’t an easy decision to make most times, so all I have to say is…GO WITH YOUR GUT. Normally, my gut tells me to stay out of it and stay in my own lane, but there are exceptions to everything. The more information you have about the situation, the more you may feel responsible to confront the cheater or tell the person that is being cheated on. My advice is, if you’re going to expose someone cheating, confront the person doing the cheating first and then go from there. 

I think we should treat others like we’d want to be treated. Wouldn’t you want to know if you were being cheated on, being put at risk of sexually transmitted diseases, humiliation, and more? Wouldn’t you want someone to tell you so you could have the information needed to decide to stop wasting your time with someone who didn’t have any respect for you? I would.