At the end of long shift, Meredith is waiting for an elevator. The doors open to reveal a cleaned-up Derek in full McDreamy mode. He’s surrounded by X-rays, brain scans and other mementos of their life at Seattle Grace. Derek shows Meredith all the people she helped him save and delivers just about the best marriage proposal ever.
"You got me into the OR. You put the rest of us to work because you've seen worse. You know we'll survive. You say you're dark and twisty, but that's not a weakness, it's a strength. It makes you who you are. I love you Meredith Grey, and I want to spend the rest of my life with you."
Meredith’s “And I want to spend the rest of my life with you” response was a long time in the making.