She picked someone else over me. Why is she doing this?

A few months ago, I asked out a female friend at work, who then strung me along (We'd make plans, then she'd cancel. repeatedly) for a couple of months until she started dating someone else. After that, I ceased contact. I deleted her number, and I avoid her when possible. Whenever we pass other though, we do talk, but I don't go out of my way to see her anymore. She hasn't said anything about it, but I've noticed she does initiate verbal contact more, and I catch her looking at me from time to time.
She picked someone else over me. Why is she doing this?
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