"Mary, Won't You Warm My Bed"

I listened to One Year last week and noticed something about "Mary, Won't You Warm My Bed."  Throughout the song, the speaker/singer explains that he's looking for Mary ("One day I will find that girl").  After the first chorus, the song changes keys, which almost represents the speaker/singer's search in a musical way.  It's as if he's lookt in A major without finding her, so now he's moving on to Bb major.