I have dated this girl almost a year?

i need your advice. I have dated this girl almost a year and although we hardly meet, but once a while we went out for dinner or movie.i have develop some felling on her. sometimes, she will also ask me for dinner.she just gave me mixed feeling.so last 2 weeks ago before i went short vacation with some friends,we have plan to watch a movie this week once i'm back. So 2 days , i sms her about our appointment and she told me that she have to check with her bf first. i was shocked coz all the while she didn't mention about it ans she told me that she know this guy for the past 5 months. i feel like been cheated and she just make use of me. Anyway, on the sms, i congratulate her. what should i do now to forget her? will i still go out with her if she ask me? or should i ask her out as usual ? I always treat her and care her so much . Its hard to forget the memories with her at the moment.