Nobody wants to find out their partner has been cheating on them. But walking in on them in the act of infidelity is an experience I'd wish upon no one, except the ex who cheated on me. Silver lining: if you walk in on an ex while they're cheating, at least they can't try to talk their way out of it (unless they're Shaggy).
In a popular Reddit thread, someone asked: "People that walked in on their SO having sex with another person, how did you react?"
1.) From SAR-Paradox:
Walked in on my ex (after three years together) with one of my best friends (at the time). Took a double take and just stood there for what couldn't have been more than 5 seconds. I then just drove back to my dorm and lost my sh*t for a minute. I've never been one to actually be out of control of my temper, but at the time, all the emotions overwhelmed me as I fell out of shock. I will never forget that moment that I felt that I had no control over my self. It was both frightening and relieving.