Why is my ex being really nice to me all of a sudden?

My ex and I work together and that is how we met. We dated for 4 months and 10 days. At one point she didn't want anything to do with me and seemed like she didn't want to talk to me. Now she is being really nice to me. I don't know if it is because we work together or she is having a change of heart with me and misses me and wants me back. Thoughts?
Why is my ex being really nice to me all of a sudden?
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