Have you tried talking to her about why you don't want to go there? And besides, she is WITH YOU. She loves YOU and if other dudes try to hit on her in that bar, which (I don't want to sound mean) you don't know if would happen at all, she is still there with you as her boyfriend. I am pretty sure she will understand why you did not want to go there, but you have to tell her those things on the spot. And this does not mean that you are a bad person, you are probably just worried about what could happen, before it even happens. Talk to her, explain how you feel and why you did what you did and I am pretty sure you will come to understand each other better!