Why did this guy from my university club go from staring and joking with me to suddenly ignoring me?

He used to stare a lot at me either from a distance or sometimes I caught him staring at me during our club events together. He used to make jokes with me, say my name a lot too, & used to be around me a lot too. He goes hey we're bumping into each other a lot lately. At one club event, I signed up but it was his friend who signed up so I was surprised to see him there too. He was like oh hey and I was like I didn't know you were helping too. His friend was joking that he took my name out and I was like what I signed up for first. He claimed he didn't see my name there and his internet sucked that day. Then at a recent event, I felt like maybe I stared at him too much or made things uncomfortable when it was just us after the club event ended. We were parting ways I wanted to ask him something. He was heading one way and I was going to the other way, but I was looking at him and he turned back to look at me.

So after that I went to the next club event but I thought he wasn't there so I left but then I saw him staring at me. But I had to go to my work study then and ironically the club event was near my work study. I would glance at him every now and then, I saw him taking solo pictures with the others across from me but his foot and his chest was pointing towards me even though he was facing the camera. I also saw him leaving with the group but he was the last person and I didn't look at him right now but I did after he kinda looked back. That was 2 weeks ago and I haven't seen him since. I have not messaged him or anything. Anyways, I saw him today when I was at the computer lobby area next to the window. I could have sworn he saw me before he opened the door and came in. I was going to say hi but then he looked upset and he was just ignoring me. I did look out the window at the other side to see he could have gone the other way to his car instead of passing by me. I don't know maybe he's really upset with me. Is he not interested anymore?

Why did this guy from my university club go from staring and joking with me to suddenly ignoring me?
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