The most common interpretation was that Angie was Angela Bowie herself, with whom Jagger supposedly (also) carried on an affair.
Angela Bowie's relevations on "The Joan Rivers Show" led some to speculate that the eponymous "Angie" was not Angela, but David Bowie.
Another prominent rumor was that "Angie" was actually about Angela Richards, Keith Richards' daughter by actress Anita Pallenberg. (This was a rather silly rumor, given that Angela Richards was less than a year old when the Rolling Stones recorded "Angie." It isn't even likely that Mick Jagger simply used her name for the song's title, as she was originally called Dandelion by her parents until she insisted on the name Angela several years later.)
Yet another rumor had it that "Angie" was about Anita Pallenberg, who had flings with both Brian Jones and Mick Jagger in addition to a multi-year relationship with Keith Richards.
When a musician composes a song about an unhappy love affair with a woman's name for a title, many of us assume it must have been inspired by a real-life romance with someone of that name (especially if it turns out he knew a girl called that, no matter who she was in his life). Yet this is often not the case; songwriters routinely pen works where names and details are chosen because they fit the meter of the composition. Although the song itself could be the catharsis of deeply-felt personal angst expressed as a specific (yet completely fictional) outpouring, or could be an actual chronicle of a hurtful experience endured, it does not necessarily follow that the gal who stirred up those feelings in real life would be given the same name in the song. Autobiography only goes so far -- if the meter is not right, the name goes. Songwriters also have composed pieces built around specific names merely because they liked the sound of them: Buddy Holly did know a "Peggy Sue" (the girlfriend of drummer Jerry Allison), but the song wasn't based on any real-life romance between her and Buddy. Sometimes musicians just write for their audiences, churning out works that expound upon common experiences their music-buying public will identify with (such as heartwrenching partings). For such offerings, the eponymous girl does not have to be anyone real, because the writer is calling upon universal themes for the substance of his song.
Was "Angie" about any one person, or was the name just plucked from the air? We don't know. But we do know enough about music not to immediately conclude that a song titled with a girl's name means the writer had an unhappy experience with a girl of that name.
Yet speculation over the identity of the "Angie" of Rolling Stone fame has long past ceased to be an active topic, a quieting of wagging tongues that has yet to take place with the original rumor, that of Mick Jagger and David Bowie having sexual knowledge of each other. Failed love affairs, as expressed in song lyrics, only hold interest for so long, but a salacious rumor about famous people engaging in a homosexual coupling will live as long as there are people to repeat it.