A "sunk cost" (or obligation alone) is a horrible reason to stay in a relationship
The "Fuck Yes or No" article, though almost four years old at this point and spawning a number of responses ("Mexican Dinner Consent" by Ferrett and "It damn well better be a yes" by me are relevant examples) has such an impact because it highlights something very important.
You have a limited number of minutes in your life. The relationships in your life, should not be ones where you simply feel obligated to remain in them.
Yes, there are obligations in relationships. Yes, relationships are not always fun and games.
But if you're in a relationship out of a sense of obligation, if you're there primarily out of a sense of duty instead of wanting to be there, then you are doing no one any favors.
You are not doing yourself a favor by staying in that relationship. You are not doing your partner(s) a favor or kindness by remaining.
At best, you are setting everyone else in the relationship for greater drama, heartbreak, and anguish when they realize that you're simply there because you feel you have to be there.
This is especially true when you may have started out wanting the relationship, only to have you, your partner(s), your goals, or situation change. Hiding that change doesn't make things magically revert back to the way they were, and the longer you hide that realization, the more likely your partner(s) are to question the entirety of the relationship.
Be honest with yourself and with those you're in relationships with.
Be honest why you're there, and why you remain there.
Be sensitive and forgiving to yourself and your partner(s) if things have changed over time.
But above all, be honest.
And make your priorities align with your life.