Are temporary, but multiple-year relationships a good thing?

I can imagine a lot of benefits to the idea of trying to find someone to remain with until old age to care for each other, but one guy I used to know was actually an older person who proposed the idea that maybe many people would be happier if they just stayed together for about 10 years (or until whenever the passion died down) and then broke up once they reached a state of disinterest and found someone new.

What do you think? Would this be pointlessly wasteful - throwing a way good relationships - or might it be a way for you to keep your life interesting?

Note that I'm not talking about flings - just relationships that last for many years, until both people get bored, and then they leave and find other people.

Are temporary, but multiple-year relationships a good thing?
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