There is always people in our lives in which we form relationships whether they be healthy or not, they are soon gone and there just people you used to know. Having lost, I relate to the feeling "someone I used to know" and its a crazy thought that someone you were so close to is now just a mere stranger. I could elaborate on this topic for hours but I'm gonna keep this short and hope you understand somewhat of what I'm trying to say.
The music video is also great, and I find it fit perfectly with the lyrics of the song!
Now for the youtube link: