It's interesting, because I find a 'prophecy' of betrayal adds this oppressive weight that's often more stressful than catching someone in the act. The dread comes from waiting for the other shoe to drop, not from the act itself. You're watching the characters navigate a relationship that's already under a death sentence they don't know about, and every little argument or moment of distance feels like a potential trigger. It completely changes how you read their interactions.
A story that used this well was 'The Invisible Life of Addie LaRue'—though not exactly cheating, that central doomed bargain creates a similar ticking-clock anxiety around love. In a more traditional sense, I've read a few webnovels where the FL gets a vision of her husband's future infidelity. The emotional impact isn't just her pain; it's watching her become paranoid, cold, or preemptively distance herself to protect her heart, which then ironically might drive him away. The tragedy is often in the self-fulfilling prophecy.