So long story short, one of my best friends has BPD. She has a crush on a mutual friend of ours and he is, by her admission, her favorite person. Him and I recently started dating and nobody in the friend group knows. We're struggling with how to tell them, but her especially, because we do deeply care about her and her feelings. She's prone to reacting by shutting down, taking everything we say as a personal slight, and generally thinking she's unlovable, etc. Recently, she's been comparing herself to me a lot and expressing that she thinks I'm better than her in every way.  I'm afraid that telling her about this new relationship is only going to confirm that in her mind. I love her dearly, and I know that I'm going to end up hurting her feelings no matter what, but would anybody have advice for the best way to tell her without absolutely destroying her? Or is this a lost cause and I'm probably gonna lose a friend?