I sent my boss a friend request on facebook and she denied it (we're both females) I've been at this location about 4 months. She accepted a friend request from a new hire that's been there for 2 months & is friends with all of my coworkers minus a few. Why did she not accept my friend request but accept everyone else's?
I feel it would be impossible to answer without having minute details about every interaction you and your boss have ever had, and these details should not be shared publicly, so we should never know.
In general though, not all people click, it really is as simple as that. This is not to say that your boss has a personally flaw, or that you do. You are more than likely both completely fine examples of the human race. It is just how things are.
Consider: Would you expect every one of your neighbors to accept a friend request?
I would let it slide and not write anything into it at all. Most times having a solid business only relationship with your boss is a blessing. The same goes for the majority of your work colleagues.
You are thinking too much.
Someone adding someone else on Facebook as friend while not you doesn't imply anything concretely. You never know what may be happening and what may be going in the other persons mind.
While no one except your manager knows what's in her mind, you should consider the following:
Work life and professional life are separate, and not everyone mixes the two.
Not everyone uses social networking sites such as Facebook with a clear cut intent. Some mixes social and professional connections, some not, while some also add strangers.
She may have not noticed your friend request on Facebook.
She may not be very active on Facebook.
She may have added the other colleague for some specific reason no one else knows.
She may have initiated adding your colleague as friend.
Both of them may be sharing a common interest.
Something else may have happened.
And so on and so forth.
So, you need not think too much as long as your work relation with your manager is going fine.