It's true, all relationships end. It's a fact of life.
That doesn't mean people can't be loving and committed and wonderful partners to each other.
My ex-husband and I had 19 wonderful years together. Even though the end was awful and traumatic, I will never call it a "failed marriage." I mean if you can get nearly 20 years of a great relationship, that's not a failure. It's 19 years of bliss.
We as people do evolve and change, and it's okay to move on and have new things.