I don't know why we put things off. But if I had to guess, I'd say it has a lot to do with fear. Fear of failure, fear of pain, fear of rejection. Sometimes the fear is just of making a decision, any decision, because what if you're wrong?
Meredith assists Derek on a patient with Parkinson's. Their working relationship is now strained, though not by their rediscovered passion, but by Bailey's knowledge of it. Bailey doesn't want Derek giving Meredith any special treatment, and despite the fact that Derek is technically Bailey's boss, Bailey's threat to keep Meredith out of surgery is enough to get Derek change his attitude around Meredith in public and not for the better. He's now intentional harsh on her. Other than Cristina & Bailey, no one else knows about Meredith and Derek particularly George, who's crush for Meredith still rages on.
Alex hasn't been himself lately. As Izzie notes, he actually seems sincere. Annie, a patient with a 70 pound tumor, takes a liking to Alex's bedside manner, not to mention the fact that "he's just so much fun to look at." But when he slips up and shows his true colors she overhears him make a snide comment about her when he doesn't think she's listening Burke tosses Alex from the case and replaces him with Cristina (even though Alex rightly notes that his flippant attitude towards patients isn't any different than hers). Cristina and George then get the joyous opportunity to hold up the 70 pound tumor during a 14 hour surgery.
Alex gets to watch over the surgical floor with Izzie, which is left understaffed as so many doctors, nurses, and interns are involved in the tumor surgery that whole day. But Izzie winds up all alone watching over the floor when Alex forgets to change the battery on his pager and doesn't get a single page from her. The floor gets busier and busier, and things reach a boiling point for Izzie when a heart patient starts dying from a massive clot that has to be removed immediately. Izzie is the only doctor around, so she has to do it herself cut open the patient's chest and reach in with her own hands and remove the clot from the heart. It's a truly heroic maneuver, and she does it successfully. But Izzie doesn't have time to revel in her moment, as she has to ream Alex for abandoning her.
Meredith is quite upset that Derek has gone from being super nice to her being a bit of a "jackass" (in her words) to her on the Parkinson's case. A procedure exists that could potentially ease the Parkinson's patients tremors, but the patient is reluctant to undergo any brain surgery particularly one that occurs while the patient is still awake. Meredith strongly sympathizes with the patient's daughter, since she's in a similar position with Ellis, so Meredith wants to encourage the patient to undergo the procedure. But Derek, with Bailey's threat firmly on his mind, disagrees with her rather harshly. Derek comes around, though, and does talk to the patient about his options again. The patient still declines, but then Meredith has some words of her own for him. And he changes his mind. After the surgery, Meredith and Derek reach an agreement no special treatment and no acting like a jackass just to appease Bailey.
The surgery to remove the massive tumor is even more complicated than they had imagined. Annie is losing too much blood, but there is little they can do as the tumor is just too entwined in her. Alex, watching the surgery from outside the OR sees trouble forming and runs to get as much blood as he can. But when he returns she's already gone. He's left there, holding the bags of blood in hand, looking down at the lifeless patient who he insulted earlier. It's a moment for him, and one that doesn't go unnoticed by Meredith, as she watches from the Gallery.
Burke finds Cristina in the on call room, where she's recovering from holding the tumor up all day. He admits to doing her a favor getting her in on the surgery, but she isn't as grateful as he'd thought a "favor" shouldn't leave her in so much back pain. They don't talk much, though, before the sexual tension between them snaps, and they're in each other's arms.