I am the Kat that Walks By Itself

it is actually what makes a marriage work.

Yes, it is. Marriage is hard work. Not all the time, but at some times in each marriage. If you've left open the possibility of leaving, you've undercut your ability to survive the hard times and thrive afterwards.

More fannishly, I don't think of OTP in quite the way you've described. It's not that there could be no other true love for the characters; it's just that I may think that within the shipping choices available, one is the healthiest or most interesting choice. It's usually the one I think has the greatest possibility to give the characters joy; which is, not coincidentally, the most satisfying choice for me.

But I will read (and sometimes write) any pairing that I find believable, positive, and potentially interesting (I confess that--to the small extent I'm interested in ships at all--I'm rarely interested in dysfunctional ships). My OTP love of Willow/Snape doesn't prevent me from enjoying Willow/Spike, Willow/Giles, or your Snape/Anya. My OTP love of Avon/Soolin doesn't prevent me from enjoying Avon/Jenna or Vila/Soolin.

Though I have NO desire to see Larry with anybody but Megan. ;-)