Flirting

Younger man trying to flirt with me. Why is he like that?

I'm confused. That younger guy is my friend's brother. He sent me first message almost one year ago. We were talking a lot. I thought he is a nice guy. He tried to flirt with me. Even he told me when I visited his brother with friends (I was 17) he was so shy and he stayed with us, because he liked me. I don't remember too much tbh, but it was cute! We met two times (one time by accident) we were talking many hours. He asked me millions questions. I wanted to ask him too so we decided to meet again. I was waiting for him in that cold winter evening, but he didn't come. He fell asleep, but he didn't feel sorry. He started to be mean. Even he told me I behave like teenager and stopped talk to me for three months. I felt disappointed and kinda sad. During that time I noticed he was seeing someone. I'm not sure if they are in relationship, but it seems like they are, but they don't show it. I can see them together everywhere also they took romantic photo session. The problem is he is trying to get my attention. He wanna meet me, but I'm saying NO every time, but he still trying to meet me. I don't send him message first also I don't answer on every his message. He is sending messages too often with some stupid messages trying to make fake fight with me, but today he started hardly flirt with me he asked if I'm single and he is interested also he wanted to meet me, but I told him NO again. I don't trust him. Why he is like that he has a girlfriend. I know he noticed me, but he didn't look at me when he was with his girlfriend he just pretend. It's not everything, but it's enough to judge/answer I guess. Guys that retard make me feel weird. I'm smiling and laughing, but I shouldn't. I'm not in love with him. But he didn't respect me before. He is just kid. But why is he like that? Is he really retarded or something?
Younger man trying to flirt with me. Why is he like that?
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