I can understand that very well. I very often feel the same way. I suspect it has several reasons with me.
Firstly, I am highly sensitive and co-dependent and constantly perceive the moods of all the people around me unfiltered and ask myself inwardly how everyone is doing, what they think, what they think about me, whether they think it's stupid what I say or do, whether the other person feels good. Secondly, I'm not fundamentally interested in all people, there are some who just find people interesting in general, I tend not to. I would like to skip the small talk part and just talk about really personal things. Third, my self-esteem is low and I often think the other person thinks I'm stupid. So, in the presence of people, to permanently hear the inner critic whispering to you, you're stupid, what you're saying is boring, you're acting weird, really robs me of a lot of energy....
With two people it works, with three people it works, but groups are so exhausting and difficult for me that I avoid such situations as completely as possible. I try to meet people only alone.
Tonight I have to go to an event with lots of small talk and lots of people. I've been dreading it for days. Keep your fingers crossed that it won't be that difficult :-)