How to forget a girl?

Pretty weird that you go with a similar theme to the game website, but still. A year and a half ago to my social networks added the girl, found out not at once, but it turned out that it was my friend early childhood. After I moved to another place, all communication with her stopped. Now, after many years she found me. Talked on the phone, texted, she always wanted to meet, to talk, but I was frozen, didn't want any relationship with anyone, even just a friendly. Even from friends removed. A year later, she called me again, re-added to friends, we're not a lot talked and discussed life's problems. And now knowing her a little closer, I realized that is very much in love. But the problem is that according to her she has a young man and she's happy with him. Since my education does not allow to go into someone else's life, I don't know what to do. Constantly thinking about her. Bad for the soul to become, when you think she's with someone else. Sit for several days in deep depression. I want her to write or call, but I understand that it will be cherevato for me the same. I don't even want another girl, I want to see myself with her. In any cases, Hobbies, not help to distract from these thoughts. Friends, looking for advice, who can faced with similar?