how to have a long and happy marriage

A French couple celebrated their 81st anniversary!

Hmmn. It might be good to marry someone with propitious prospects for living a long time. For instance, shorter people tend to live longer. Also, Japanese women have the longest lifespans of anyone (and, concomitantly, they tend to be not particularly tall), but since that is presumably due to a combination of genetic and cultural factors, the effect is almost certainly diminished for Japanese-American women. So, marrying a Japanese woman in Japan (and not tampering with her diet by introducing, say, bacon sushi) might be a way to nab a long-lived partner.

There are also people who restrict their caloric intake to 800 calories a day, based on research that shows that rats live longer when deprived of calories, but none of them have been doing it long enough for anyone to see if they live longer. And who wants to be married to a sprout-eating weirdo anyway?

You could try marrying a short person, feeding them more sushi, and rescuing them from being hit by buses.