I am a sucker for slow corruption, when executed correctly, showing the wife/girlfriend gradually changing from loyal/loving partner to distant/corrupted acquaintance. Finding the clues that hint something is happening is quite thrilling. Reminds me of the feeling of anxiety mixed with arousal when doing stuff in public, and there is a possibility of getting caught.
Clothing/Behaviour → Everyday clothes become more and more revealing, wearing sexy lingerie, which MC doesn't personally see/enjoy. At first, the wife/girlfriend is somewhat reserved/shy, but later on she becomes more depraved/perverted.
Silhouette/Hidden sex → Seeing silhouette/curtain sex or partially obscured top/lower half, and acting and sounding really suspicious. I enjoy both when ordinary stuff happens, but it looks questionable behind the curtain, and there is actual sex, but the MC is unsure who is behind there.
Phone/video calls → Strange sounds, moans, muffled speech, technical interruptions happening during regular audio/video calls are great. If they are actual sounds, moans, and voiceovers, that elevates it to another level.
Aftermath → Noticing damaged clothing, stains, pubic hairs, dripping liquids, messy hair, used condoms and so on is what gets me going. Initially, MC gets a believable excuse, but that becomes less so as the corruption goes on.
Mystery NTR → MC discovering or receiving lewd pictures/videos of a friend's girlfriend where she wears blindfold, mask, has her face obscured while in the act. Jewellery, clothes, proportions pointing to the girlfriend's identity is chef's kiss.
Depravity → The wife/girlfriend is pushed to do sex acts, she doesn't do/enjoy with MC, but starts to crave with the antagonist. As the corruption progresses, she's instructed to be less sexual with MC, or even start withholding sex.