My boyfriend and another girl

My boyfriend used to be interested in this girl before he met me, though he never told her that he liked her and he doesn't know if she was interested in him. She was supposed to visit him during Halloween. We all live in different states, him in Texas, she's in Washington, and I'm in Florida, and she came up with the idea of visiting him. They have known each other for maybe two years? but neither of them followed up on the meeting since he met me before October; we fell for each other during Hurricane Ike. They have met once in 2007 in Las Vegas along with a couple other people from our former WoW guild.

He has told her that he's in a relationship with me around the time when he visited me for Thanksgiving, but they have talked maybe two or three times only in the past few months. But suddenly she wants to visit him and possibly another friend in his area in February for her 21st birthday. Should I be worried about it? I trust him but I'm worried about what her intentions are. I have heard she was into the roleplaying boyfriend thing in World of Warcraft and had a relationship in game and in real life with the former guild leader. My boyfriend took over the guild lead for a while after the first leader quit and she talked to my boyfriend a lot before I met him. I don't know if she's the kind of girl who flirts with officers/leaders because of the appeal of power (yes I know it's a game but some people get too involved in it).

So should I be worried about her? I probably won't be around to make sure she doesn't try to make a move on him and since it'll be her 21st I assume there will be drinking. =/ I honestly wish she would just drop the idea and spend her birthday up in Washington with her friends and family there.

I'll definitely try to be there if she goes through with it. She texted my boyfriend asking if he'd be ok with her spending her 21st in Texas. I talked to him briefly about it, asking what was said. He told me she hadn't replied after he said he was ok with it. I know she tends to get really busy with classes in Washington so I guess it would just be for a weekend? He said she would probably stay in Austin if she did come (he's in Houston). I don't know if since she hasn't replied yet if she'll follow through, but I plan on talking to him about how it's odd for her to spend her birthday with someone else's boyfriend instead of family. I don't want to get too over-protective in case it is just a 'friends thing', but I really don't trust her.

Advice?

Your boyfriend needs to enforce the boundary that is you two as a couple. If you do not feel comfortable with her spending time with him alone, then you should tell him this. Either he will respect you, or he won't. If he doesn't, it gives you a good understanding of where you sit in the relationship.

Just tell him that you are worried that she might hit on him.
There's not much he can do, he can't really say "No you can't come to Texas because my girlfriend doesn't want you to.".
I don't know exact locations, but I know that there is a fair distance between Texas and Florida. How are you two trying to make this relationship work?

I believe that you should only be in a long distance relationship if you are very serious about it. WoW isn't a good base for a relationship. Do you have plans to live in the same state in the near future?