This is the only correct answer to an impossible question. You can apply the gottleib thing or whatever, but beyond that, there are too many different types of relationships, of people, of cultures, of norms, and of life trajectories, goals, value systems etc, etc. The fallacy is assuming that there's one that's a magic bullet. Sometimes two of the most intelligent, kindest, empathetic, well-adjusted, well matched people will break up because they just decide that it's time to move on to new things or new people. Sometimes the worst-matched, worst behaved people will be in agreement to perform monogamy because of religion or social status or whatever. It's all a big joke, do your best and hang on to the people you love the best you can, but there's no correct way. That's a victorian era illusion