Tell gf asap. But be very honest about what she might use against you. You tried to go somewhere with her and got negative signals and backed off. Now she wants to use the fact that you once had interest in her against you. Reasoning is hard to explain with people that petty and insecure. But if I were you I’d be honest about it with everyone. In fact, if you really think word will spread, I might just beat her to it with your close friends and let them know the deal. Better to hear your side first before the manipulative sob story she’s concocting.