There I a girl who I think might like my boyfriend. She only ever looks at him when with a group of friends. Her body is always turned towards him, and I noticed that she doesn't always hear other people, she seems just focused on him. Wtf? I'm 100% sure my boyfriend loves me and has no interest in her but it's annoying watching her do that. What can I do?
If your boyfriend is not interested in this other girl, then what are you worried about? Do you trust your boyfriend?
To be honest just ignore her, speak to your boyfriend about it and let him deal with it. The real issue here is about your insecurity dealing with other people, don't let it get to you, its all part of a relationship and building that trust.
Why should you do something? Could be you're interpreting her actions wrong. But if you are sure she's into your boyfriend, why should you do something? She knows he's taken, I hope she has some common sense to stay away from him flirtwise and your boyfriend loves you, isn't interested in her. I don't see anything you should do.
I have been in your situation and the other girls situation. I would say the best thing to do is keep him close. If she starts to talk to him or you see that he gets distracted, ask him if there is anything going on. If you don't want to do that, just keep an eye on things, and if anything gets suspicious look into it further.