Aaron Carter was overcome with emotion after he was embraced by the crowd in a gay bar where he performed ... the first such appearance since he came out as bisexual.

Aaron performed at Hamburger Mary's near his hometown in Brandon, Florida, and dropped the new song "Hard to Love", written about his ex-GF.

It's touching and pretty funny, as Aaron scopes out the crowd for hot guys ... and at least 2 catch his eye. But he sees another dude and takes a pass.