Love triangle and the ring!!!?

Me and my brother compete in kickboxing games and usually I win most of the games that I face against him. Recently his girl friend who is very cute proposed to me but I did not reject her as she was in my mind for sometime. Now the problem is we are in love but my brother is the only obstacle. He has found out about our affair and is threatening that he will hurt his former gf. I am really concerned about her. He is jealous about this and very serious about our affair. Pls.advise.