I don’t regret any of the relationships I’ve been in. They’ve all made me into the person I am now, and I’m sure that at the time, starting and ending them made the most sense to me.

Sure, the failure of a relationship doesn't mean the relationship had no value, but the expectation that a happy marriage lasts your whole life is the very foundation of marriage. "I was committed for 5 years and then I wasn't" is as affirming to a marriage as "I honored your warranty for 5 years and then I didn't" is to a lifetime warranty. If you just wanted to be in a relationship with someone that realistically lasts 5 - 10 years, you don't marry them.

Every aspect of marriage hinges on it not ending before death. All religions explicitly spell that out one way or another. Religion aside, legally every government imposes life-changing financial penalties for ending it that way. The main reason governments do this is because culturally it was very common for the wife to stop working or stop pursuing a career in a marriage due to the implied commitment the husband has to the wife, but if the wife knows that the relationship has a 5 year clock then she would behave differently. Married couples have children due to the implied permanence of their relationship, if a 5 year expiration date was known upfront it would change behavior because it's well known that divorce is damaging to children.

If I buy something called the Forever Car that's very expensive but promises in return to never break down, and then it breaks down in the middle of an interstate trip...I guess that doesn't invalidate all the miles the Forever Car got me through, but it certainly calls into question the value proposition of the Forever Car. I may not regret that I bought a car but I certainly wouldn't have gotten a Forever Car. I would definitely say that a Forever Car that doesn't go the distance has something very wrong with it because it doesn't deliver what it promises.