I'm in high school, and my friends range from 16-17. There's currently 5 of us. (1 guy, 4 girls including me) So the sixth (guy), whom I'll refer to as Z if needed, started acting weird when schools reopened almost 2 months ago. He didn't hang out with us and was basically giving us the cold shoulder. Mind you that he's the only one in our group who is in a different class, the rest of us share a class, but we hung out together in the morning, break times, and after school.
So we were all confused as to why he was acting this way. When we'd greet him he'd look pissed or just moody. He hung out with us once on the first week of school, and he was quiet and distant (as if waiting for us to ask him what's wrong) but then he eventually stopped for good.
So I was seeking reasons as to why he was doing this and then I heard from a mutual friend that appearantly he stopped hanging with us coz he felt "left out", which is not entirely untrue. I notice that sometimes the group leaves him out, like during convos etc, and I try to make him feel included, and we had a good relationship. So this went on for weeks; he stopped texting, exited our main group chat recently that we'd created to make plans to go out together, and now we don't know if he's still coming or not, and just went full on MIA.
Some of my friends stopped caring about the situation and aren't really looking for closure.
But this is where the weird part is. Now when we walk passed him at school he'll wave and greet us with a smile, like nothing is wrong, and maybe even try to make some small talk. My friends have agreed that it's weird indeed. His friendliness is off putting because how can you act normal to the same people you stopped talking to for weeks without any disclosure??
I just wanted to hear some outside opinions because Im having a hard time figuring this out. I don't like talking to him normally because it feels weird as hell