"Introverts want company just as much as extroverts do, but they prefer it in either short doses or with people they know well."
Remember that this week. When someone turns down your party invitation, don't take it personally. More often than not it is because they want to spend some time alone or with another close person. Respect their decision and even encourage it and you will get a very loyal friend. That's not a bad thing to come out of a rejected invitation.