L sees the girl and wants to meet her. Time stops for 60sec and he sees their entire relationship play out right up until their break up. Because their relationship is doomed he decides to get up and leave his ring (by the way you never see it on his finger until he puts it on in the alternate timeline). In the current timeline (where they have yet to meet) she sees the forgotten ring and tries to give it back to him. L tells her to keep it because he already saw that they would break up. When she looks into his eyes she she is able to see the alternate timeline as well. This is shown by the alternate timeline video reversing quickly. This also resets the timeline so that they never meet. The scene where L offers her umbrella is the first time they would have met IF he decided to go with the relationship. But because he doesn’t he ends up alone. GENIUS!”