I saw him with a girl today. If he has a girlfriend, why was he acting so flirty towards me?

I saw him at a shopping mall. At first I thought the girl next to him was his niece or something, but the girl had heart-shaped balloons in my hand. He also had a lot of bags in his hand. He didn't see me, but the girl took him by the hand and took him to the cinema. I felt really bad, I was starting to like him. At first he was very curious and affectionate towards me, but all of a sudden he became very cold. Is it because he got a girlfriend? And also his friends always looking at me but ıdk them What is that meaning?

I saw him with a girl today. If he has a girlfriend, why was he acting so flirty towards me?
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