*shrug* - maybe it's because I had a lesbian couple as room mates for a while, but I picked up VERY quickly in the OP that this was a quad-X chromosome relationship situation, lol.
I'm going to echo what a lot of others have said - just bring it up. Subtely or bluntly - that depends on how you two talk about things otherwise. But do it. It is scary, but its a lot easier than it seems.
Think of how many of your statements/quotes were along the lines of "why don't they just" or "wouldn't it just be easier/better if they". From the outside looking in, miscomminications between couples or friends or any cloe group look simple and silly; in the mix, they're intimidating and scary. Rely on the connection that has kept you together for so long to make sense of the subject, and go for it.
Frankly, based on what you posted, I think you're both in a veyr similar mindset and are both scared to just elevate the topic. Total conjecture based on incomplete data on my part, but call it a strong gut feeling. She'll be more receptive than you are worried she'll be either way, because she loves you.