Why is that when a man's words and actions don't match?

We met at work and soon became colleagues. He would often ask me to catch up everytime we spoke on the phone. He always used to give me these big smiles whenever he saw me. Well he is ignoring me now, I don't know how to react. Later I found out he has a girlfriend. I'm not sure if I'm angry or sad because I feel like he kinda leads me on. Why is he doing that? Why can't he just cut me off completely from him? I stopped talking to him now.
Why is that when a man's words and actions don't match?
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