HELP WITH MY GIRLFRIEND?

okay so this is what happaned, i finally got together with the girl i liked afterr 2 years. Over these past 2 years she had a single boy friend. He was not very nice,and they split there own ways. They were also together a year before i entered this school. During that time this bad boyfriend had a best friend, he lives in arabia now. they were such cool friends and he was good friends with my gf , but he moved away. Her original bf also moved away. And so after her break up she was completely free of these two. And we finally got together. Now i hear this friend from arabia is coming back, and i was okay with it, because i thought they were friends. But apparently this guy wants her now, she told him shes taken and loves me only, and so he decides to pester her about dumping me.she still relents, i told her to ignore him and try to avoid him because he doesnt like you having a relationship with any other guy cept him, /she then says she cant do that, because she considers him her "brother" i told her that she didnt find anything wrong with hanging out with her " brother" who totally wants to hook up with her. What should i do?