This is a classic "She's gone" tale. The person you care about has left you all alone and given you no explanation. The feelings and thoughts that go through your head when you are searching for a reason why.
lyrics
I know that you're gone
I could see it coming closer
Thought that we were warm
Now I see it's boiling over
Remembering the nights
I knew that no one did you better
Now I'm turning out the light
Cuz you never even left a letter