As much as it hurts to hear it said, the best course of action is to get her out of your life. She had no qualms about cheating on you and lying to you. She just wants to use you for emotional support while she sleeps with this other guy, and that is nowhere near fair on you.
Ask yourself whether you want her back because you still care about her, or because you're afraid of not being with her, afraid to be single again, afraid of change and new things. Don't be sucked into thinking that you'll instantly feel better if you get back together.
Even if you did get back together, could you honestly trust her? You sound like you were struggling to make it work at long distance anyway ... your friends are right when they say that you should let it all go. Block everything, get rid of all the photos and ignore any attempts to contact you.
I know it sucks because you liked her, but she really isn't going to be worth it. She made that choice, not you.