What should I do? I'm still in love with her but my friend doesn't care!?

I recently went through a break up with my ex, not that long ago. I was with her for quite some time. We were even talking about our future but eventually she dumped me. Eventually she started apologizing to me and telling me the mistake she made. And right before she was about to come back to me, my best friend flirts with her and wins/steals her. He knew I was not over her and I told him that but he's like "I don't care, I like her so get over it..." I seriously love her more than he ever will. And the other day, I secretly heard a conversation between him and his friend and he said "if she breaks up with me like she did to justin, I don't care." He seems to not care about her and just want a relationship. I wish she could realize that I'M the one who truly loves her. My friend aka her new bf doesn't seem to give a crap about her but I'm afraid if I tell her, she'll think I'm jealous and purposely trying to break them up. I want her back though. I can't believe he did this... ={