Yes, "working" at a relationship is tiring, and after so many years, boring. It's better to quit amicably and avoid a bitter divorce. Breaking up may be hard to do, but at least it's doing something; it's not passive. I hear all this.
But folks should hang in there for the sake of together forever romance, and of mature unconditional love. I don't want Angelina and Brad, I want Jennifer Aniston and Brad Pitt.