I really appreciate everybody's comments.
In particular, though, I want to mentioned GroundedSpirit's advice. I ended up having a conversation with a friend who is monogamous but poly-friendly and we came to a similar conclusion. Rather than get wrapped up in labels, I'm just going to look for somebody I can have a deep connection with. If that person is happy with an open relationship, then great. If she's not... I'll have to cross that bridge when I get there, but taking positive action is better than sitting around feeling mopey.