Modern marriage is definitely a mess, as it's mainly a legal entanglement with the government. I know sites like this always talk about women who chase alphas while keeping a beta to support her, but I don't really care about that. Because first off, I'm not going to tolerate being cuckolded, and secondly, those girls are slvts anyway, and ultimately I don't find slvts appealing.
Marriage made more sense in agricultural times, because a man could raise sons to help plow the field, run the farm, and protect the land. In that sense, I don't even see marriage as being monogamous, a lot of men used to have multiple wives. The more wives, the more children. I don't think polygamy should really be illegal in the US, I don't see a good legal reason for it (not that I want multiple wives myself). Feminists paint these kind of arrangements as "monstrous", but if it works for those involved, it must be okay.
People in such times also used to live more spread out. A man (or woman) growing up didn't see six million people of the opposite sex running around all the time. There were only a few good options, so they were more of value to each other. Now days everything is disposable, including people apparently.