Lost in relations, how to get over it?

So, basically I am in this country (Ukraine) for 3 months (summer) . And my friend introduced me to few more people. 3 girls to be more specific. 2 of girls are cool and I am talking with them fine. But another one I kinda like her, and even though I know I will never be with her since I don't live in that country, and she has like 8 boyfriends in different cities. I still like her. She talks and acts to me like to a friend. TO a real friend. Like she sees when I feel bad, she usually comes up and talks to me and helps out. But every evening she calls her bf to come hang out with us. I can't start protest against him not to come because she will go away then. So she always sits with her bf and does stuff like hugs , kisses etc.. And I don't know what's that feeling called but when I see him with her I just start hating her and him. And everyday on my way home, I am thinking ok I am not going out tomorrow **** this world. And every evening when she calls me to come out I just can't refuse and I come out, and then the crap evening starts again. She doesn't call me during day, if I call her she says she's busy even though I know she's at home because I see her online. So she just calls me out on evenings is it on purpose to annoy me if she noticed I feel crap when I see him. And even though I chose my life so far to be alone without girlfriends, I still can't get over it. What should I do? Today from anger I even said **** off to all my friends and left, and went to local statue of Lenin and sat at it sitting for few hours in darkness looking at stars. So anyone please help?