In love with my best friend’s boyfriend

This is quite a long story, but is is info that you need to know to understand the problem.
My best friend is very insecure, so every time a guy does nice to her, she ”falls in love” with him. I don’t mind that, not at all, if she wants to. But she has had 3 boyfriends in the past month, including my own brother. She knows that she was wrong at that time, but now there is someone else. This guy has been nice to me for a long while, and I spoke to him a lot and now I kind of fell in love with him. But my best friend got to know him a month later and fell in love with him too. Now because I am very shy, I haven’t told him, that was very stupid. My best friend has now got in a relationship with him, because he said that he fell in love with her too, even though they didn’t really know each other. I was still in love with him, not as much as before, but still. So one day he was hanging out with me, he said ”It really bothered me to know that you weren’t in love with me”. And of course I told him that I was, even though that wasn’t so smart. And he said he was in love with me as well, but because he thought I wasn’t, he moved on. And now we really want to get together, but my best friend is absolutely all over him, and she likes him so much .. I absolutely don’t want to break her. But now her boyfriend also said that he didn’t feel the same way about her as he felt before, because he got to know here better now. And she doesn’t know anything about this.

I don’t know what to do, the only thing that will happen is that he will break up with my best friend, but, should I go and date him? It’s mean, but, would she understand? I mean, she’s the one that always likes my friends. I just hope that there is a way everything will be ok.

Please help me, it will be very appreciated.