At the end of Season 2 we saw Christina dealing with a lot of her internal problems regarding her relationship with Burke. Simply--he's ready to stop sowing his wild oats and plant strictly in her fields. I don't think Christina has anything against Burke in general but she's so wrapped up in herself that until he was in his death throes she was just kind of sterile. In Season 3 we predict that she's going to break it off with Burke and explore some other options. She's not going to actively pursue other people but, like Burke, they will just end up in her lap (possibly literally). I've also heard rumors she might get with a girl, though not one on the current staff. Guess we'll have to wait for Season 3 to find out.