That's a common issue with people suffering from loneliness. I've often felt that way myself, to the point where I'd rather be by myself rather than around people I can't relate to.
Indeed I have. Though I find it's more prevalent when it's a group of people that I don't have anything in common with. I can't really talk to them so I stay quiet and then I get bored, then I notice I'm not partaking in the conversation which makes me feel lonely and isolated. So yeah, I've felt that before. I just... do my best to hang about with people who are my age group, or have my interests, then I don't feel so alone.
Yes. I'm very different from the rest of my family in that I lack the social ease and clever sense of humor that they have. I don't feel as out of place when I'm with someone who is actually a friend to me, but I don't function well in groups of more than two people because I don't have a very strong speaking voice. It amazes me how people can converse in such large groups and just talk and talk and talk.