If a guy acts very reserved around a girl? What does that mean?

Anonymous
We were both shy at first but he ended up being really friendly and acted super giddy. After meeting I noticed him looking at me and he tried to get closer to me, sat/ walked next to me. We met up again after awhile and this time around I tried to be more friendly + outgoing. But he ended up being really quiet and serious. With everyone else he was joking and being himself. I thought he looked like he hated me from how tense he was but I haven't done anything wrong to him. He even walked away in the opposite direction like he was nervous to see me when I came over to him and his friends. After that it has just been weird behavior. He also did a double take while walking past me recently. He has friends that are girls and he is fine with other girls he has just met.
If a guy acts very reserved around a girl? What does that mean?
3 Opinion