Do you get a "subtracted you as a friend" message?

I am not *new* to facebook. I have been facebookly active for a couple of months, but I am still learning a few things and getting accustomed to the exponential interconnectedness of it all. I have one friend who is a co-worker. I had another friend who is friends with him, send me a friend request. (Confusing, yes, that's the way the facebook is.) I know her because she was my child's teacher one year and she also went to my church once. I don't know her very well, but have always really liked her. She seems like someone I would really want to be an actual friend to, so of course I accepted her friend request. I assumed she found me through my co-worker, P.

When I would look at P's page, it would show her as our only friend in common. When I would look at her page, it would show P as our only friend in common. As of a couple days ago, I noticed that it is not showing me either one as a friend in common. So I went to each of their pages, and looked at their friend lists, and neither one lists the other as a friend anymore.

I feel kind of like a stalker, looking at who they are friends with, and dwelling on it. But I feel a little confused. How do you unfriend someone on facebook? And why would you? What sort of offense would it take to unfriend a facebook friend? I mean, I have people I have kind of regretted befriending, but I can't see cutting them off as a facebook friend.

I have a couple religious people that are always writing religious updates and such. Most annoying is someone I don't think I have seen in person since grade school. I barely remember her, except that she was annoying and smelled bad. When I got a friend request from her, I thought "well, I can't smell her through the computer, and how much could she annoy me on facebook?" It turns out she can annoy me a lot actually. What's weird is that she doesn't even say anything to me directly, it's just that she joins so many groups and becomes a fan of so many things, that for awhile my whole page of information was listing all of these things. But then I discovered that I can choose the option of seeing less information about this person. Problem solved. Now it does not tell me anything about her, but she is still listed as my friend.

I am wondering should I ask my coworker friend about this relationship change? Is that being too nosy? On facebook, you can see everyone's friends and who is interacting with who, so is there any privacy? I'm just not sure how I feel about the facebook world. And how it merges with the real world.