To those who replied...
Thank you for your concern.  Being at work in the middle of a 60+ minute call is not the ideal time to get such e-mails.  No way to escape, no way to express anything, & leaving isn't an option.  This was my only option.  I really do appreciate the responses, it helped a lot.  For the record, I'm home now, & things are a little clearer.  Having had time to think about it, I realize that she's done this many times before.  At least three times that I can think of right off the top of my head.  If I choose to pursue it further, she'd probably change her mind.  She's very fickle that way.
However, my sister posed a very serious question: Do you want to pursue it further?  In the state it's in right now, I do not.  I'm tired of riding the roller-coaster, one minute she's debating children's names & the next she's wishing her boy toy would invite her over for another make-out session.  If a month from now she decides she's through playing games, then I'd definitely re-consider.  But for now I think I'm going to write her back (or maybe call her, but that would make things unnecessarily rough) & pretty much say "OK."  I don't feel like arguing it, I don't feel like making a big deal out of it.  In a way it's almost a relief... I didn't have to do it.  She did it for me.  I'm not to blame, I kept my promise.  Now I get to find somebody else.  Not that I want anybody else, I want my best friend.  But such is life.
Pretender...
The moderator removed the first word of my subject, which was a slang term for a plea to God to banish this situation to hell.
Oh, and one more thing for the record... I won't be 19 until June.  Which brings up a whole 'nother issue... The women who ARE emotionally mature & know what the hell they want wouldn't give me the time of day because of my age.  So I'm stuck, really.
Viper GTS