I think it also comes down to self-confidence, if you know how she feels about you and obviously what you give her, you really have nothing to worry about. If it was an issue, get it out in the open and see where her motives lie.
Like Nick said, if she's attractive she'll get attention, it's what guys do. The way I've always tried to look at it, especially when you trust the girl, is no matter what is said or what those other guys may think in their heads, I'm going home with her.
If you trust her, talk to her about it and put yourself out there. If you don't then find someone else that doesn't make you feel that way, keeping in mind that if it keeps happening its something you will have to deal with.
Just my 2 cents.
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