First have you seen any animal being with only one another physically for the rest of life, humans are also animals but since we are intelligent we have set some boundaries and made some rules after marriage but now people are breaking those boundaries emotionally maybe they'll be for the rest of life but physically it's impossible for few people women need multiple dicks and men need multiple pussies, 2nd some men have this fantasy of watching the love of their life to get fucked and treated like a whore infront of them no matter if they have big dicks