a sad song that I listed to/ watched and didnt get at first

im not sure about how to add a video, so im sorry! but if you a=want to hear the song and see the video pleas go to this site:
http://www.youtube.com/watch?v=L1SZvhCNIY0


So my sister played this song for me called "what sarah said" by Death Cab for Cutie. I didnt really understand it untill I listened to it a few times and talked to her about it and watched the video, but the video majes it alot more emotional. Its about a guy, who loves a girl (sarah) and theyv had a discusion previously about dieing, and she says that it is tru love to watch someone die becasue everyone wants to die with someone who cares about them at their side. So when the time comes, and she goes to the intensive care unit, all he thinks about is what she said. He just sits in his chair thinking about her question; "whoes gonna watch you die?" so while everyone els is freaking out and being sad and scared about their loved ones he thinks about how he treated her, and about how much hes care for her.

Im not too sure about what the end of the video means and neither is my sister so if you figure it out could you tell me?