Meanings of "drift apart"
When a couple in a relationship that were initially very close start to loose interest in each other usually by being very different to start with, or because they may be selfish, or a lot of times boredom with everything and developing new interests that are not shared.
"drift apart" in lyrics
I take a slice of the moon and I put it in the sangria
If I walk off it will be to hear you saying you are mine
Why do I go till the edge of the world if you drift apart
After all the one-off destination is wherever you are