Bye Bye Black Bird

I have this habit of saying this phrase if anyone is leaving for good. I don't know why. When my friend took off to Illinois last year, I said the same thing to her "Bye bye black bird" Same goes if someone is getting married and settling for good me also will say the same phrase. Some of my friends are puzzled as they didn't know the exact meaning of the phrase. Me also have no idea why I'm saying it smoothly without hesitation. It's spontaneous.I guess, black bird has something to do with me in my life before this. Well today, I have someone leaving me again for good. I'm gonna miss him. My very true friend, indeed. And he is away now. Without me having a chance to pat him goodbye. Bye bye black bird.