Green’s Dictionary of Slang

(US) to habitually frequent bars.

1952		J. Jones From Here to Eternity (1998) 687: That would mean his usual evenings at the Club for poker and bar-flying [...] could not be counted on to give her a chance to get away.
2012		T. Robinson ‘So Long, Johnnie Scumbag’ in Dirty Words [ebook] What I needed was a drink. As it was, I interrupted my day's barflying to see Johnnie.