I did read one that worked for me at the time, back then, at the time being in season 4 - "Halfway" by Ariana. If I were to reread it today, with the entire series canon in mind, it probably wouldn't work for me anymore.

And, err, the third of my AUs actually has them have sex, but let's just say that this is not a happy occasion. And no, I don't think they could ever "gotten together" in the sense of becoming a working couple. Mind you, the fifth of my AUs gives them a stable relationship but of a different kind, and it's in its way the darkest of the lot. You'll see what I mean.*g*