In which direction do I go with her?

My sister had been pestering me to get me to go to a group called young life, which I had avoided due to its religious connotations, (I'm atheist). Eventually though, prom was setting to roll around, and she said that there was a girl that would be interested in going with me to prom. I finally caved, went, had a good time, but said girl was at a football game. I got her number from a mutual friend, who encouraged me to text/call her. We talked for a bit, and I saw her at the young life meetings for a month or two afterwards (her parents hosted the meetings at their house). Afterwards she and two other friends, along with myself would go to sonic for drinks and whatnot. We always had a good time, and eventually I worked up the courage to ask her to prom. She accepted rather cheerily. We texted more in between, had more young life meetings, worked out prom details, and I called and asked her to a movie (prom was a few weeks away). She agreed, but we couldn't fit it in until after prom. No big deal. Prom was a blast, and I got the sense that we both had a rather good time. I gave her the movie details one night, and in the middle she asked if some friends we both knew could tag along. I said yes, as she wanted to combine movie plans with them (at least that was her excuse). We had fun, but I didn't feel like anything happened at the movie. I believe she used to have an eating disorder, so I wasn't terribly dismayed when she turned down my offers to share my concessions (or the fact that she didn't eat a ton at prom dinner). Things continued rather well, we continued our texting conversations, and we saw each other again at the young life BBQ in the park.I tried to set up plans with when we could go out (as I had wanted to go to the movies with solely her), but it didnt work out right, as it stormed rather severely). Eventually I was able to nail down that we could meet up after memorial weekend, and after attending her grad party, I texted her today. She was working, so I kept the conversation brief, but asked her to drinks at sonic (with just me), since it had been a while, and that would be a comfortable situation for us. She agreed, and mentioned that her boyfriend could get us free drinks. In my mind I started freaking out, but internalized it and managed to kindly agree and ask her to let me know when she was free to do so. I am confused that I was unaware of this and am unsure of how to proceed. I don't read into facebook too much, but her status is single and shes never mentioned a boyfriend before or shown obvious affection to a particular individual in my presence. To be honest, I feel like all this time has been somewhat wasted, and don't know what to do at this point. We're both going to the same college this fall, and I don't know who this guy is. Should I continue to do things like text her regularly, ask her out to stuff, etc. and wait it out or maintain a friendship and look elsewhere when I get to college? What do I do?