Invest more fully in the relationship you already have. No person ever stays the same and every relationship evolves and changes. She isn't the same person you met years ago; get to know her all over again.
Talk more, hone your communication skills, see where needs aren't being met, romance her, ask yourself where your feelings can deepen, examine your impatience and see where that's coming from, figure out what kinds of boundaries and agreements you'd want in a poly relationship and discuss them. These things take time -- just because you want it now doesn't mean it's best for you to have it now. Make an agreement to revisit the poly discussion down the road a bit. And keep in mind that Genebean might not ever feel comfortable with poly, and she doesn't have to agree to it, which means then that you both have some important choices in front of you.
The world opens up... when you do.
Oh, oh, can't you see? Love is the drug for me. ~Bryan Ferry
"Love is that condition in which another person's happiness is essential to your own." ~Robert Heinlein