My best friend/girl I love just told me she's anorexic!?

I'm 14. SHe's 13. We're both girls. I'm secretly in love with her and she just told me about this. She's always pretended to looooove to eat abnormally and eats all the time but apparently after she eats so much with me and others she'll starve herself for days after! She's terribly depressed and I know how that feels. I want to help her but I cannot go against her! I can't do it! She's beggining me not to make her stop and I love her to much to say no but I love her to much to say yes! I don't want to make her do something she doesn't wnat to do but I can't let her continue doing this to herself! She compares starving herself to cutting yourself (which I used to have a problem with). I know what she means by it makes thigns feel better. But I can't let her hurt herself anymore. What am I supposed to do? I haet having to go through this alone!