Flirting

Is she using me or just keeping me as a future option?

So I've known a girl for a few years now and when I tried to let her know I had a crush on her she told me she thought I was just a friend. We have hung out, just the two of us since then. I also picked her up from work early when she was sick. Then she had stopped taking my calls or answering my face book messages. I did ask her if she was OK and if there was anything I could help her with, but she didn't reply. I even apologized because I thought she was ignoring me because of something I did. Turns out she had a boyfriend for about 2 months, I found out on my own. She didn't say anything to me about it. Around a week later since I sent her a message, she replies. She says she is OK, there isn't any serious problem she is in. She also said I shouldn't get mad if she doesn't reply to my calls or messages. She ended the message by saying that she will send me a message and we will meet up soon. I suppose she doesn't know that I know she has a boyfriend. A week later I sent her another message asking how she was and if everything was still OK with her. No reply. I know she has seen the message, and I know she hasn't stopped replying to any of her other guy friend messages since she had a boyfriend. I don't know if she is trying to not hurt my feelings or she doesn't want to tell me because she wants to keep me around as a future option or she's using me?
Is she using me or just keeping me as a future option?
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