Netorare hentai (寝取られ), also refered as NTR or cuckold, is a genre where the intent is to cause an emotion of deep jealousy or distress in the reader.
Most common theme is when main protagonist’s loved one is seduced away by another guy, with or without their knowledge.
There is also Netori. It’s when the protagonist steals the lover or wife/husband of someone else. It’s light side of dark sided netorare.