What should I do!? I'm having major trouble.?

I'm best friends with this amazing kid, let's call him, Josh. Josh and I love each other, but we're not in love. We've been best friends for almost a year now. Everything's been going great! Until he started being best friends with this other girl, let's call her, Rose. Rose and I aren't friends. Not since she started being best friends with Josh. The one thing that bugs be about Rose is that she thinks she own Josh. She doesn't respect that Josh and I are best friends. She thinks that I'm just a piece of **** (excuse my language), and it pisses me off. Rose is stuck up. She thinks everyone's friends with her, when in reality, everyone hates her. Josh doesn't see what I see. He sees Rose as an amazing girl, but he thinks that I'm more amazing than Rose, which is good. I've talked to Josh so many times. I've tried to tell him what I'm feeling, but he still doesn't see it. I've also told Rose how I feel. She just doesn't care. I really need advice on what I should do, and to stop being friends with Josh, well that's just not an option.