I'd say it's too early in your relationship to be considering her a serious girlfriend. So what if someone else becomes her "primary?" Labels suck. Just worry about whether or not you get your needs met. Oh, and keep looking. It is harder for guys to meet women in general, but you have to put yourself out there in all possible social situations, as well as online at OKC, etc. Good luck.
Independent solo polyamorist seeking lover-friends willing to invest in friendship, companionship, and love, but without a need for partnership.
Never confuse commitment with exclusivity, love with ownership, nor sex with intimacy!
For me, it is far better to grasp the Universe as it really is than to persist in delusion, however satisfying and reassuring.
~ Carl Sagan