So here's how you know something's wrong with you.
You make tentative plans with a friend that then become solid. You are going to hang out for a weekend, but not the entire weekend, because the last day of the weekend the friend has family stuff to do. No biggie. The friend can arrive anytime because they are not tied down to a departure time. Loose plans are made to do fun things, but nothing specific or rock-solid.
Later in the week, you get an IM from another friend mentioning something about hanging our this weekend. Just as you are about to say you have plans with visiting friend, they ask if you got the e-mail. So you say no and go check your e-mail. You have an e-mail from a different friend saying something about the friend who is coming to spend time with you (and the one that just IM'd you) wanting to spend time with them.
Here is where things go awry.
Your first thought is: Well, if she wanted to go hang out with that other friend, why did she accept MY invitation?
Then you re-read the e-mail and see that you are also invited, as you are included on the e-mail and also asked if you have other plans already with the visiting friend.
Your next thought is: They all obviously already MADE plans to hang out with each other last weekend when they all spent time together. I was not involved in those plans, nor was I told about them when I spoke to visiting friend. So it seems I am an afterthought.
You try to work through these thoughts and figure out why you feel this way. Clearly a gut reaction. Clearly not entirely rational. But it's the way you feel. You feel like visiting friend doesn't really want to spend time with you, she wants to spend time with the other friends. And the only reason they asked you along was because visiting friend told them she was going to be visiting you. So leaving you out wouldn't be very polite. You try to think about how you could decline and they could go on their merry way and have their desired night out. You feel tiny and unimportant. You feel somehow rejected. It all makes little sense, but it makes total sense. In your head.
Then you write about it in your LiveJournal.