Are relationships meant to be a life-long commitment?

One of my friend's philosophy of relationships is to commit once, for the rest of his life, expecting his partner to do the same. I definitely don't doubt the necessity of commitment in a relationship, I'm just bugged-out by the "for the rest of life" part.

Through thick and thin, better or worse -- this is quite subjective isn't it? I mean if you're in a strained relationship because the both of you are working your asses off to make the family work, maybe that'll be a good definition of sticking together through hardship. BUT what if one bugger decides to just sit on the couch and watch TV all day, with no care in the world for making ends meet? Would that still be worthy of "through thick and thin"?

Does this line apply even if one half stops putting the effort into whichever part of the relationship?

Look back to a year or 2-3 years ago? You're not the same person are you?

We're all constantly changing due to the different environments that we're in or experiences we go through. You're currently with whoever you're with
because you're happy or there's some other form of a positive result from the relationship (in this moment) isn't it? But what if you and your partner change over the years but in ways that push you further away from one another?

If we don't even know where or what WE are going to be in 5 years time, how would we know we would be a suitable partner for our partner? How would this form of commitment work without feeling like a dead weight? Where did this "commitment" custom come about, why was it created? Why do people adhere to this? Where are the origins? What are the reasons for it? Are the reasons for it outdated?

Walk on the paths as they show themselves

You can only live in the now, and the future is always uncertain. Should we be placing such pressures of "forever commitment" on ourselves?

Maybe we should take today and decide to be a better individual, a better partner, be committed in THIS moment, be happy and healthy. We can't control the future but we can control our thoughts and feelings in this moment. These "future problems" may or may not happen, so why add it to our list of things to stress ourselves right now?