Just let me kick my $0.02 in.
Believe it or not, I was in your situation not even 3 months ago. However, unlike you, I didn't publicly express my rage. It took me until about a month ago to stop my depressed thoughts and wake up from my horrible rage. While I still feel saddened by what I contemplated, I'm very glad I didn't. I'd have missed all this wonderful stuff and all these wonderful discussions.
Yes, it is truely sad what she did to you. Whenever (we'll call her Diane) Diane finally told me why she spent all that time with me, I seriously felt like completely abandoning all ethics and actually beating her face in. Thankfully I didn't...
Well, after I spent a good week harbouring that psychotic rage, I cooled down enough to think of it rationally. After about a month, I realized that I wasn't angry at her, but at myself. Then I realized that it wasn't my fault that she did this to me, but her fault for doing it to me. I mean, what sort of person would ruin their friendship just to spite someone (in my case, she went back to her boyfriend after telling me all that. Supposedly I was the test to see if she really loved him or whatnot. Bunch of {censored} if you ask me)? I then realized what a disturbed person this was, and felt genuinely sorry for her.
Anyway, she's still one of my best friends (although certainly not my best), and every time she args me off, I always play the "deception card" (ie I threaten to tell her boyfriend all that she did to me). In the meantime, I'm still trying to help her out with whatever disturbed stuff she went through (because even though she suppsodly proved her love, she still doubts his. This is why I don't like HS relationships. Too much bs for me. Either you love someone, or your simply using them for your own aims. There is no middle!).
Of course, every time I look at her, there is still the reminder of such deception, combined with the memories I thought we had. My solution (if you have an equal problem with facing the person still):
don't look at her! It is sooo much easier to talk to the person (and thus communicate what happened) if you stare at the wall behind them instead of at them. Sure, they might wonder why you never make eye contact, but just say that you don't want them to get any ideas that your staring at them for less-than-proper reasons (that excuse worked for me, especially considering that Diane is extremely paranoid about guys who look at her for long periods of time).
If that doesn't work, pull an intentional Fruedian Slip on her. In other words, abandon all caution and place your feelings (love, not the suicidal stuff) into actions. Instead of simply running around smittenly, confront her, describe what you felt whenever you found out what she did, then tell what you felt while you thought she liked you. At the very worst, you'll lose a friend (which, as it stands now, in all honesty, would you want her as your friend?). At the least, you'll get what you felt in the open and you two can work it out.
My point is, don't take what she did personally. The fact that she did this alone means she's pretty disturbed. Further, the fact that you were third in line points to some serious committment issues and male issues (by male issues, I mean to say that psycholocially she may be using men like this to "get back" at them for something that happened in her past. I recommend you ask her if she ever had problems with her father or other male authority figure. Try to ease her into this, for if there was a problem it will undoubtably be painful for her to admit it. Still, if there is a problem, it needs to be addressed so she can stop the self-destruction).
If you need help working it out, or simply want to do it in a neutral way (which might actually be preferential, as you could get it all out in the open without worrying about what the other would say), start a thread on here and get posting. While I'd like to offer my help (after all, I do have recent experience in this), I'll understand if you'd lock the thread and throw a password on it (if you can't do it, I'm sure Ildurest would be willing to make a thread up for you and you could change the password later). The point of it all is, if you don't communicate what happened, you'll just start running down a slippery slope.
In any case (physically confront her or digitally), I'll throw out some general suggestions in case you need help:
Remind her that she's still important to your life
Tell her how you felt whenever you thought she was your girlfriend
Tell her what the experience meant to you
Tell her what you felt like whenever you found out this stuff
Forgive her
Ask for her forgiveness
Offer some time to think it over, but agree that in the very least, you'll try to maintain at least a platonic relationship (ie just friends)
Offer to help her through her own emotional crisises (which are fairly obvious if you consider the fact that she had to two-time her boyfriend, then two-time that guy, then abandon all three of you)
Forgive her (yes, this is mentioned twice. There is no point in harbouring rage against her and there is no point in remembering a sad event. Remember the happy times and forget the rest).
Hopefully, you can salvage the friendship and at least get things close to normal. While you'll probably never forget the experience, you'll definately learn from it. Hopefully you won't get any negative ideas towards women because of this (I'll be honest, during my "week of rage", I was probably the biggest chauvinist to every women I came in contact with. Definately not cool of me to do, and I'm still apologizing for it), and hopefully you can help her out with her problems. Of course, if all this fails, you'll at least know a little about how messed up people can be, and know that maybe, underneath it all, she might not have been the person you thought her to be. It's better to know now than years from now, when you've practically your entire emotional self into a sick joke of hers (
sorry, that was a more personal comment, although I suppose it might still apply to you. So, I'll leave it in, just in case).
Glad you're feeling better, and we all admire you for your intelligence. You're probably one of the most intelligent people I know of, including the so-called "genii" of my school (sure, they might have a 5.0 GPA, but they've no idea how the world works). I'm honoured to know you, and I'll tell you this: whenever an adult talks down to you for no apparant reason, be sure to tell them that you're intelligent enough to know that they're talking down to you, and that you don't appreciate it. If that doesn't work, tell them that we all make mistakes, and that he/she shouldn't expect you to be some superhuman, omniscient creature (be sure to scream at them while saying that).
Stay strong and don't feel afraid to emote as needed (in private of course, not in the middle of the food court or whatnot
) over this. It takes a bigger man to show how he feels than it does to bottle it up until it explodes in a bloody rage that ends in 30 dead and hundreds wounded.