3: "Not Those times. Not One Line. Don't You Dare."
It's an interesting quirk of the way the story is told that Silence in the Library and Forest of the Dead actually improve with time as we shift from seeing the story from the Doctor's perspective to seeing it from River's. We know from later events that River's greatest fear is the day she looks into the Doctor's eyes and he doesn't know her, and the real twist of the knife in that moment is that we know we already saw that happen
and we didn't care. We didn't
know enough to care at the time. But go back and revisit the Death of River Song now, now that we've seen what she's seen. At the risk of getting all 'math-y', Happiness and sadness are very much like a sine-wave. What I mean is - the degree to which the line can rise above the axis into 'happy' must be matched by the degree to which the line is willing to dip below the axis into 'sad' They have to balance. The Doctor is desperately offering River here the chance to just cancel the wave and stay alive - but without either the sadness or the happiness. Just staying alive for it's own sake. And River quite rightly tells him that the joy he's brought her more than makes up for the pain.