No one has mentioned the elevator scene??
When Meredith swallowed her pride and quitely said "I miss you" my heart broke for her, then seeing the the indecision and naked need on Derek's face behind her... awww. It's her that he wants but his loyalty keeps him trying with his wife. Their relationship will blow up very soon. When Addy called Derek out and said you are either in 100% or you're out she was right. He's decided to work on his marriage, he should really be working on it. IMO He's still to pissed off to give their marriage a fighting chance, not to mention his overwhelming feelings for Meredith.
In the end I hope his sacrifice is worth it