Egg, I totally agree with your reading of that line. If you have a dirty mind, so do I. (There is nothing spoilery about this response, so I have not put it in a spoiler box.)
As for who will find out first? I go back and forth between Catherine and Brass. For seem reason, I feel like Grissom is the one who would spill, and I feel like, if he spilled, he would spill to one of these two.
I guess someone could just sleuth it out, too, but Grissom and Sara do such a good job downplaying their lurve, that I think one of them is going to have to talk in order for their relationship to become common knowledge. And if someone is going to talk, again, my money's on Grissom. I think Sara would rather walk over hot coals than compromise Grissom, while I'm sure Grissom would bank (rightly) on Sara's forgiving his blabbing.
Just a theory.
Now to wax rhapsodic about GSR.
GSR saved CSI for me. I've shipped GSR from the get-go, but by season 6, I was despairing. There were a few times that season that I just didn't watch an episode, because the hermetic closure of the classic procedural was feeling stale, and even forgetful of the promise of past episodes. (How could the events of Butterflied or Committed not precipitate more?) But then, as season 6 drew to close, the GSR returned, the episodes became far more compelling, continuity ratcheted up, and I recommitted to the show. Now I enjoy watching CSI as much as I did at the beginning. My love for the show, which was fading, was totally resurrected. I have loved this season, and it is totally because of GSR and the show's new dedication to continuity and subtly drawn narrative arcs. Some people think that GSR has had a negative effect on the other characters, and even on Grissom, but I feel that the effect has been only positive. I've really loved all the characters on the show this season in a way I haven't loved them for a long time. Greg has been great, Nick has been great, Catherine has redeemed herself in many ways. Heck, I even feel like I might like Lady Heather a little. And that's saying something.
I feel this season has shown the perfect balance of contained episodes and narrative arcs (Greggo's, Grissom and Sara's, the MCSK). It has all of the drama and none of the lame of most other serial dramas. For me, the show is a million times more interesting in its current format than is a standard serial (Grey's Anatomy) or a standard procedural (Law and Order.)
Did I mention how that's all due to the positive effects of GSR? Long live GSR!