I think this song is about a destructive relationship (romantic or a very close friendship). Both people love each other, but they are both so deep down in darkness (depression/sadness etc.) that they can't help each other. Probably, the narrator was affected by the other person to fall in to the darkness, hence the first two lines.
The twilight is a symbol for how they are stuck in a situation that isn't downright horrible, the twilight is just a big nothing, so they can't really end it. In the end, they get out of the twilight by accepting the darkness, because that's where they find each other.
I think this song is about a destructive relationship (romantic or a very close friendship). Both people love each other, but they are both so deep down in darkness (depression/sadness etc.) that they can't help each other. Probably, the narrator was affected by the other person to fall in to the darkness, hence the first two lines. The twilight is a symbol for how they are stuck in a situation that isn't downright horrible, the twilight is just a big nothing, so they can't really end it. In the end, they get out of the twilight by accepting the darkness, because that's where they find each other.