Just my $.02...
If she's the one you've always talked to, try talking to her about it. Ask her up front if there is more than friendship going on over there. No accusations, people do "drift apart" especially as they go to different schools, different jobs, different life experiences. If you, or she, can't talk openly about it, you may have your answer right there. If it comes to that, where you're not the only fish in her sea, so to speak, remember, She's not the only one out there, either!