This is just my personal opinion, and others may not agree but a humble suggestion - and involves some of what others mentioned as buildup:
Cheating and slutty sex aren't taboo if they happen all the time, it becomes the norm. The hottest scenes are always the FIRST ones, where the gf/wife/fiancee has been eternally faithful, then finally finds herself on her knees in front of a beefstick. But in too many games I find once they get far along into the "corruption" path, its just a 24/7 all-out slut fest and I get bored quickly and not turned on, it's too mechanical- "Oh, yet another gangbang?
"
It's kinda like how seeing a girl naked for the first time is so great, because it's unwrapping this forbidden taboo present underneath. If she walks around in string bikinis everyday, there's less of a transition. (not that I dislike string bikinis, I like them, but if I know I'm going to be seeing someone naked, I'd almost rather her have more on because it's a bigger switch, if that makes sense). Same is true for corruption - it's far better if the wife starts off extremely well-mannered and not unkempt.
I don't know how this could be made into a game mechanic, but maybe if there was a clever design with some time of cooldown resource like "taboo" or "chance to cheat" - it would be
very enjoyable for me to see a game where spied on your girlfriend cheating on you having hot sex, then instead of banging everyone in sight she promises you she's changed, and acts like it for a few weeks, then out of the blue you catch her again.
Just recognize like many things, corruption can be a limited resource, and it can be difficult for a writer to keep increasing the stakes after she's already done everything. The answer is, you don't, you either reset or move to a different character.