I am not sure that your core assumption, that you can find one person, while both in your 20s, who will meet all your needs for the next 60-80 years, is a reaso

I am not sure that your core assumption, that you can find one person, while both in your 20s, who will meet all your needs for the next 60-80 years, is a reasonable one. When we look at the origins of the "life partner" assumption, they are grounded in a time when people lived in a much more networked social environment than today's. In other words, people had many more outlets for social and emotional contact, as well as more hours working - and probably spent much less time 1:1 with their spouse. AND the overall social and cultural milieu was much more stable than it is today.