Major fuck up, ouch. Putting on my eastern european chick expert hat ... they have no concept of men and women being "friends". East european guys (as shes already told you) play the field at every opportunity and shes just assuming you are doing likewise.

My advice for getting her back is to throw away the PUA handbook - make a grand romantic gesture, send flowers (odd number of roses) to her house saying that your going to take her out on saturday to buy an outrageously sexy pair of high heels. Even if she tells you shes still not interested, turn up anyway and don't take no for an answer. With an EU its not over until she has told you to piss off to your face.

Remove her mate from facebook. Warn all your female friends not to post personal messages on your FB wall (or remove any likely to do so anyway). Talk and explanations wont cut it, EU girls expect to see actual demonstration of intent.

For future reference Dont FB/txt/email/phone any of her friends, ever except in the direst emergency, and never let her find out that you spent any significant one-to-one time with any non-family member woman no matter how innocent. Going "out for a drink" with a female friend for example is an absolute no no. Don't txt/phone/email etc any non-family woman in her presence. Bring her flowers and chocolate at least once every week or two. Open doors for her, take her coat off and pull the seat out for at restaurants, help her out of the car when you stop, always offer to carry her bags. Compliment her frequently. That should keep you in good shape