Girl's Behavior

Why did this girl become super cold towards me after that?

I was new to my workplace and I met this cute girl there. I had a little chat with her and the same day I wanted talk about something personal about new workplace. (She was the only girl I trusted with it) It was urgent to me. So I made a call to a guy who worked with me there and asked her number. I didn't even know her name. This guy sent a number and I made call to that number. I could get the information I wanted from that girl too. But I was talking to her thinking it was that girl. The girl I wanted to talk. The next day I told it the male colleague. I am sure he told that to the owner of the number. That girl was friendly towards me. Later she became so cold... more like she hates me. She is married as I know.

Why did she behave like that?
Why did this girl become super cold towards me after that?
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