Babylon is used here to represent the ‘’Babylon the Great, the Mother of Prostitutes and Abominations of the Earth‘’, commonly known as the Whore of Babylon (Which is also the name of the artwork they used as the cover for the song), refers to a symbolic female figure of evil, mentioned in the Book of Revelation:

“[…] And I saw a woman sitting on a scarlet beast, full of names of blasphemy with seven heads and ten horns. The woman was garbed in purple and scarlet, and gilded with gold, gems, and pearls, and bearing a golden goblet in her hand full of abominations and filthiness of her fornication.” – Revelation 17:3,4

The “Whore of Babylon” is being used by the Boy$ to talk about getting away from their exes and gold-digging “hoes”, as said in the line:

Still I deal with trauma from this ex in my past
Only bitch I know psycho enough to land me in rehab