Unless you're sure about he or she is really the one you want to spend your lifetime with or it'll definitely ruin your relationship. How romantic that a couple was once each other's best friends, whatever it takes. So glad I'm still think this way.
How can it be a happy ending story?? Where is the human princess? Things won't be so easy. The prince will choose a princess, not a mermaid. And where is her pursuit for the real soul? Anyway, true love conquers all.