Dating is in
Course of Temptation (RPG/Sandbox), no marriage though as the game is simulating college life at a very free-spirited university. No NTR content AFAIK.
I think
Masters of Raana (RPG/Management) lets you marry. Some religions allow you to have more than one wife. Not sure if there are repercussions if you fool around with other characters while married. No NTR content AFAIK.
Free Cities (Management) lets you marry your slaves. Probably also has Netorase, since I don't think there's anything preventing you from assigning your slave-spouse to the brothel or club. Recommend the popular mod that shall not be linked for more features.
Not much content yet, but in
Power of Will (CYOA) you start out married. Not sure if there's NTR, but maybe? The game describes that one of your assistants has the hots for your wife, IIRC. The wife can also have different personalities, e.g. one where she encourages you having fun with other women, while in another she seems oblivious so far.