There's no dignity in dragging along something that's dead.
If you and your partner have been "working on your problems" for more than half of the time you've been together, that relationships isn't working. If most of your lovemaking is "makeup sex," then it isn't working. If you two are more like roommates than friends, it isn't working.
People like to feel self-righteous about their relationships withstanding the test of time, which is bizarre for a number of reasons.
First of all, everyone knows that terrible relationships are capable of lasting lifetimes just as much as those borne of true love; the length of a romance has nothing to do with its quality.
Secondly, it creates this weird idea that some people are more adept at romance than anyone else, which is a ridiculous myth we keep perpetuating for some reason, and results in so many people feeling as though they are inherently flawed when their best efforts still result in a breakup.
The truth is that some couples have the right chemistry and interpersonal dynamics to work for the long haul, and some simply don't. A lot of times, a relationship's dissolution really is as simple as two people not working well as a functioning unit, no matter how much love or best intentions those involved may have.
There's no dignity in dragging along something that's dead and forcing a relationship that's not working out. It turns both partners into people they aren't proud of and usually don't respect. Despite what you may have been lead to believe, there's no reason to be proud of maintaining a relationship that's more misery than contentment.
Love isn't a marathon, and emotional strength isn't synonymous with seeing how long you can endure discomfort in a situation that's meant to be nurturing. Arguably, it takes a lot more courage to walk away from someone you love but aren't happy with than to let your relationship slowly dissolve into something ugly and full of vitriol.
Strength involves looking at a relationship objectively, and deciding to take care of yourself if you find that you have lost yourself in an unfixable romance. Releasing the other person to find someone more compatible to his or her chemistry is also an act of incredible love and kindness.
It hurts and it's difficult, but it takes enormous courage to stop struggling and give yourselves both the chance to be happy and in love, even if it isn't with each other.