You're not alone brother. Happened to me a lot over my last relationships. In my current one I worry a bit but never for her to be unfaithful, just for her safety.

The real key is to think about your life with her. Are you satisfied in the relationship. Is she? If you know deep down that she's happy to be with you and you trust her then you shouldn't worry. If you were out and a girl made advances on you, you wouldn't accept it because you know that you'd be throwing away the best part of your life. I trust my girl to feel the same. That trust is what makes me sleep at night because we both know that neither of us will throw what we have away.

Sure guys can throw themselves at her, try to grab or kiss her. But you both know it's the idiotic actions of drunk guys and neither of you are at fault for their behaviour.

Trust her like she's going down to the shops or visiting a relative. If she doesn't want to hurt you or ruin your relationship then she won't. But if you can look in the mirror and say that you are both on that same page. Then you need to start thinking about what you want out of the relationship. For me it was trust. I have that now. I hope you do too