Down to references to the singer being "broken" when they met, and "I was sinking, you were rising," (John was sinking in depression and purposelessness; Sherlock was rising in his profession)

And "you were the missing link that helped me break my chains."

https://www.youtube.com/watch?v=6nqdcbFU9Bg&feature=kp

Because of the line about "lay beside me", it does imply the singer and the dead person had a romantic relationship...but...just barely. And it's definitely about a death rather than a breakup.