From what I saw in the manga, Yuuki loves both of them (this is my opinion).
From what Kaname say, we see that Yuuki loves both of them, right? Between Kaname and her was always a distance. I want to say that they two could not communicate freely. Yes, is true, Kaname loves her, but, in my opinion, it was as if he had a small obsession for Yuuki (this appeared on the forum – I do not know where, but I read it-) and the result is that I am not the single person which think like this.
Oh, Kaname have such a lovely, beautiful and poor face *smile*. Ok, sorry, back to topic. This face tells us that Kaname yearns for her more that anything – yeah, I know, I just repeat what others said.
I do not have to tell other reasons why Yuuki loves Kaname, right?
When I first read some chapters, I clearly said "Yuuki loves Kaname", but after I thought for a while and I reread, I noticed that Yuuki loves Zero. After reading chapter eighty-one, I am unsure of Zero’s feelings towards Yuuki. Now, seriously, he hates pure-bloods, right? And then... Why he drank Sara’s blood? He did not think that he betrayed Yuuki? And he took Sara – a pureblood - to the Association! I think that he is getting crazy and crazy! Ok, I understand, Yuuki told Zero to protect Sara, but he drank her blood!
Yes, I know, I got off track from the subject. In my opinion, she loves both, but they treat with indifference those feelings .
Now, I hope not to start fights because of what I wrote.