Evidence suggests the virus has indeed been around longer than imagined since the 50's, probably. 

As far as the gay population, the only biologic link I have heard of was a reservoir in Haiti.  At one time it was apparently a favored destination for gay holiday/vacations, and many of the local Haitians were already infected.  If gay vacationers got infected there, and brought it "back" to the US, that might have been one source.  Research has definitely shown that unprotected anal receptive intercourse is the most at risk form of sexual practice that can transmit the virus from an infected human being to another. 

Gene