Both suggestions from both of you don't fit with my observations at all. People that do actually found families are overwhelmingly faithful in monogamous relationships, complete penguin style with house, dog and kids. Yes, yes, of course every second couple has a secret BDSM-basement and countless affairs... or maybe not. I think the evolutionary explanation we often hear are mostly horseshit to be honest and wouldn't even make sense since humans need decades to mature.

The only trend I see is that people not married by 30 mostly aren't going to do it later and in many cases the men and women don't even want a relationship anymore. The sudden decision of settling down after having countless relationships is certainly a lifestyle lie to yourself and others. Just accept that marriage might not be for you, which is completely fine. Contrary to popular belief there is no pope forcing you to marry anyone. Some say there is societal pressure, but your mom and dad aren't society.

Maybe these impressions actually do stem from porn although I don't really believe that either. Lifestyle choice seem to be primarily influenced by class and education. Maybe porn consumption is too, but I doubt it.