I didn't realise they were kissing. I thought they were just hugging: Lelouch comforting Shirley. But now that I watched the scene again, it's totally obvious. Hmm... Well, Shirley should have been in a pretty witless state, so who knows, Lelouch might be able to avert responsibility once he decides he can't leave the rebellion. Since he was so shocked about the dead of Shirley's dad, that should only bolster his wish to keep Zero's business apart from his cover business (being a student and all that jazz), and having a gullible, innocent girlfriend wouldn't help, I think. Could be hard to explain where he's disappearing all the time.