Christine and The Phantom from 'The Phantom of the Opera'
I know Raoul is boring, but come on! Christine, you’re pretty and you can sing stuff! You MUST have had better romantic prospects than “that guy who lives in the basement”! Besides, not only does Erik (otherwise known as the Phantom, or the Opera Ghost) knowingly foster a disturbing co-dependence, but he murders people to further Christine's career and kidnaps her multiple times. That's not a relationship; it's a hostage situation.