"Sixes and Sevens" is about feeling lost in life and estranged from someone important. The latter is not central to the song but comes through in the line, "I found, I'm lost in your reflection, I don't know why." Mostly, the song is about being generally lost and trying to make sense of life.
The title comes from a common UK idiom meaning confusion and disarray. According to World Wide Words
, there are three potential sources for the saying. One is the Bible's Job 5:19, which reads (in King James Version), "He shall deliver thee in six troubles; yea, in seven shall no evil touch thee." Another is a 1484 dispute between two livery companies in London - a dispute that ended with a judge ruling that the Merchant Taylors Company and the Skinners Company would alternate their positions of precedence every year, meaning that one would be at six and one would be at seven.
The most likely explanation pins the point of origin to a game of dice called Hazard. Within the rules of the game, rolling fives or sixes was the most improbably bet, so anyone who made it was considered foolish or confused.
The game was originally French, and the saying "to set on cinque and sice" (French for five and six) became popular. As time went on, the saying evolved through English misunderstanding of the French to become "six and seven" and was separated entirely from the game in which it originated, because seven cannot be rolled on a die. At that point it became just a general term for confusion.