I feel constantly left out and hurt by my friends, is what they did wrong?

I don’t know if this is the right subreddit to post this, but whatever.

I’m still in school, and I’ve made a group of friends, but everytime we are told to get into groups of a certain number for school projects, and there’s one person in the friend group who has to be kicked out. It’s always me.

Although I hate to admit, I’m a very sensitive person. I act like i don’t care every time I get left out, but inside it really, really hurts me, but I never express it to others. They don’t know my sensitivity and probably never will.

I get even more upset when I expect them to at least apologise or ask the teacher if they could include one more person. While I’m about to burst into tears, they seem to not really care at all, I don’t think they understand how I feel at all either.

I suffer from extreme social anxiety. At school, you have no idea how hard it is for me to make conversations, or talk to people in general. I act like an extrovert on the outside, so I doubt anyone actually knows I have social anxiety. Now that I realise that my existence never actually mattered to anyone, hurts. A lot.

To make matters worse, they even created a group chat without me (we have two group chats, im not in the other one)
They claim they never text on it, but i doubt that. Their reasoning was because I was annoying.

As im a very sensitive person, i don’t think they realise that, and based upon this personality I’ve been showing them, they assume that I won’t be affected.
It’s quite obvious they never realised my feelings or the many nights I’ve spent crying. They don’t know, and if I told them that I was hurt by that, they probably wouldn’t understand, and blame it on me, and never think that they were in the wrong.

Regardless, they are truly good people, although it contradicts what I’ve been saying, they are nice people and have great personalities. Not all of them are like this, some are actually amazing and kind people but never speak up whenever I’m left out. I have a knack for forgiving people, usually after a day or so, i blame myself for being sensitive and continue to hang out with them only to get hurt again on occasion.

This happened today, right now I’m incredibly hurt, because they left me out and talked to me again like nothing really mattered. I’ll admit once again I’m probably quite sensitive, honestly I just see them as fake but at the same time I don’t blame them and consider them my best friends.