Hey... this is a pretty tough situation. Is she happy with this man? If it seems that she's really happy, maybe it's better if you keep this to yourself. If you tell her, it just might make things very complicated for her, and then she'll have a mess on her hands. If you REALLY love her, you'll be HAPPY for her, even if she's not with you. I know thats really tough because I'm going through this now and I've been through it before, but love evolves to more mature levels, and you'll learn to love her this way. Best of luck!
Most of us go to our grave with our music still inside of us.