The Protagonist remains sympathetic if they cheat, and becomes an innocent, wronged victim if they are the one being cheated on.Bisexuals are portrayed as incapable of faithfulness or have merely informed sexuality, and men are more prone to having affairs than women (and often portrayed as The Unfair Sex too when it comes to cheating).Perhaps things haven't been going so well with Alice for some time.Maybe they just had a major fight and Bob stormed off.For extra scumbag points, he may be keeping Carol similarly in the dark about Alice.Chances are he'll eventually get caught; if he didn't, the story wouldn't have the same dramatic impact. Way back in the day, when marriage was considered permanent and divorce was a word whispered fearfully by gossiping old ladies, The Affair was a shocker of a storyline, and very often an automatic Moral Event Horizon for the cheating partner., but the heroine is much more likely to end up happy this way.However, it creates a problem insofar as the heroine has to neither fight her common sense nor reform the hero for a Happy Ending.
Often, a sequence of "get together → one cheats → they break up → they make up → the other one cheats", and so on) will be followed so often and so tiresomely that it becomes a Yoyo Plot Point.
But here's the thing: Bob doesn't tell Alice about it.
He doesn't dump her, he doesn't tell her that he thinks the marriage is on the rocks, he doesn't talk to her about Polyamory or swinging, he doesn't even ask for "more space".
Amy: You know when sometimes you meet someone so beautiful, and then you actually talk to them and five minutes later they're as dull as a brick.
Then there's other people, and you meet them and you think, "Not bad, they're okay," and then you get to know them and, and their face just sort of becomes them, like their personality is written all over it, and they just, they turn into something so beautiful ... Sabine: Sure, women like me swoon for a hero, but that's only because deep down, we think we can change them. I want a nice, safe, reliable mass-murderer that I can depend on.A few rules usually hold true in fiction: If a woman cheats, her paramour just scored a victory over her cuckolded husband, who is now permanently dishonored.