Why does he still keep trying?

He has a girlfriend and kept pursuing me for months but I refused to have something casual with him or to get involved in any way because I don't want any kind of drama. However, he still continues to talk to me. He left the office where we worked together recently but still wished me on my birthday this week with hearts emoji and gave me wishes. I don't understand what's up with him. Why does he still want to be in touch with me when I have made it clear I don't want anything with him? I have been ignoring him for the last 2 months and had stopped talking to him but still he keeps trying?
Why does he still keep trying?
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