This song has a bit of a split meaning for me, depending on my mood... First, there's the common thought that it implies death. Someone you love has suddenly passed away, maybe even by suicide. The bit "But though you're still with me, I've been alone all along" shows this, that even though you're going to remember them you never really knew them, because they never told you how they really felt.

My second interpretation of this song is of somebody who's been ditched by their best friend. Somebody who's been abandoned by the person they've gone through everything with. All you can think of is how you've done everything for them and still love them, but they don't want or need you anymore. You'd love to move on, but you keep remembering how much they mean to you...

Of course I may be totally off, but what's music for? Relate it to your life