I've been flirting with someone and we've discussed dating, but he hasn't told his girlfriend

My partner is fine with me dating my crush, but my crush hasn’t told his gf he’s poly. He’s continuing to flirt with me while also delaying talking to her. I’m trying really hard to get him to talk to his gf cause he’s being a dick to both of us by not telling her, I’m tired of being his secret, and I don’t want his gf getting hurt. So I guess I have two questions: 1. Am I also an asshole in this situation, for letting things get this far? 2. How do I get outta this mess?

I don’t think you’re an asshole - it sounds like you were acting in good faith, expecting that he’s going to talk to his girlfriend about permission to date you. And now that things have gone this far, you’re realizing that they shouldn’t go farther without her consent.

Let him know that you’re no longer comfortable with things as they stand, and you feel dangerously close to being complicit in his choice to cheat on his girlfriend. Tell him that everything between you two needs to halt immediately and can only resume once she’s fully informed and on board.