My friend has a girlfriend still he gets pissed off if I stop contacting him why?

Last Christmas he didn't wish me and I didn't wish him. We both did it deliberately unaware of each other's intention of the same. He was pissed about me not contacting. He has a girlfriend and hmmde clear he is in love with her the. Why he pissed about me not contacting
My friend has a girlfriend still he gets pissed off if I stop contacting him why?
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