Why dont you just ask your gf to tell you honestly how she'd feel about you pursuing something with her gf? Then see if the gf is actually interested. As for how to introduce her, use her name, or "my friend, ___", or "[your girlfriend's name]'s girlfriend, ___."
The major players. Me, 30ish bi female. Gia, girlfriend of 4+ years. Clay, boyfriend/dom. Davis, ex/friend/"it's complicated." Eddie, roommate & fwb.
The supporting cast. Eric, Gia's husband. Bee, Gia and Eric's toddler. Dexter, Gia's lover. Helen, Eric's lover. Izzy and Nikki, Clay's partners. Liam, Eddie's husband.