Should I be worried? Should I do something?

You should be concerned but if you have trust in your boyfriend then You should have nothing to worry about. If I were in your shoes I would at least keep tabs on her, but Trust your boyfriend to make the right decisions. If your love is as strong as you say it is, then Don't worry about it.

Keep your friends close, but keep your enemies CLOSER (that way you'll always know what they're up to). If she's a newly minted single freak, than you definitely want to at least keep tabs on this one.

You should be able to use you female instincts to determine what her motives and new feelings are (if any) if you just spend time with the both of them and observe their subtle interactions (how they look and speak to each other, how they include/or ignore you when you're around etc. ).

You probably should be scared, but if he truly likes you then he wouldn't cheat. Just call him some more and try to get together. I know you live far, but it's better to show that you are trying to get together.

First and foremost, no matter how insanely jealous you are of her, don't let it be obvious or complain about her to him. At first he might assure you that you're the one he wants but if you keep it up, he'll get annoyed by it and he might even get curious about her. Like, hmm 'if my girlfriend is soooo worried there must be something interesting about my friend. Let me check it out' and that might draw them closer and eventually together. I'm not saying ignore the situation, just be smart about it. I know how frustrating it can be when the person you care about is far away (been there) and as much as you want to spend more time together for whatever reasons you can't. I know how easy it is to picture scenarios in your head about him and another girl. I mean, you're here, he's there. He's amazing, gorgeous, perfect (to you) why won't other girls want him and why wouldn't he want someone who's closer to him? Try to avoid those thoughts, trust me, I get them too (the guy I'm really into lives 2 hrs away from me) and it just makes things worse and you see things that aren't really there. Just try and find ways to spend more time with him and hopefully he'll reciprocate and visit you more often. Watch out for any real changes in the way he treats you and if he suddenly becomes distant towards you (make sure it's NOT in your head). Is he spending all his time with her? Has he stopped calling you a lot? Does he act cold? Does he talk about her non stop? Does he AVOID talking about her all together? See, talking TOO much or TOO little about her can mean something. Have you caught him lying about hanging with her? If the answer is no to all of these questions, then relax. It's ok to talk to him about it, if you see something weird, if you know she's pursuing him, you can't keep it bottled up either, just make sure you don't go crazy on him. If he says there's nothing to worry about and that he doesn't want her, he wants you. Believe it and drop the issue. Unless you catch him cheating, then that's a whole other story.