Let's take a look at the verb drift and the phrasal verb drift apart:
Drift (verb) - When something is carried by currents of water (or air) it drifts. The water moves it, usually slowly:
"Didn't you notice that the boat was starting to drift out to sea?"
Drift apart (phrasal verb) - Slowly cease to be close to or friends with someone; lose personal contact over time:
"The two men, who had been friends since school, drifted apart after they started work."
"We used to be big friends, but we drifted apart after he moved to a different town."