I need HELP! its about a boy and my best friend?

ok, me and my best friend both like the same boy. he's going out with her, but she's saying she'll dump him for me. if she dumps him for me, she'll end up hating me, if she stays with him, ill end up hating her. so its a lose lose situation with the same outcome either way. the thing is, i think i'd be more unhappy with them together, than she'd be with them apart. i think i could end up killing myself over this, whereas thats something she'd never do. as for the boy, he'd be happier with her, but this is killing me and i cant deal with them being together but i dont want to lose my best friend. what should i do??? PS. yeah, they both mean a lot to me, and i dont mean to be selfish, but i dont want to be unhappy. PPS. we're a trio, another best friend is in this, rachel, and if we end up hating each other, this would absolutely KILL rachel, because us being a trio is the only thing keeping her alive, basically (shes suicidal)