Too lost in her..

I'm going to try and make this brief. Basically I have feelings for one of my best friends, but she is (as always) straight. And I've always been ok with that. I've liked since I met her, but (unlike previous straight-girl crushes) I've never let it consume me.

She confided in me recently that she's battling a serious illness, something she's not told anyone else. Its made me realise how much she means to me. I can't imagine life without her. I'm totally getting lost in my feelings for her now though, and feel like I need to distance myself from her. But she needs me more than ever now so I just can't do that. At the moment, she's all I think about. I need to be able to support her, but at the same time need to get over her because I'm really struggling to hold it together.

The whole situation is making me want to tell her that I love her (i really think i do) but at the same time, I know deep down that I don't want to tell her. To be honest, I think she knows how much she means to me and no good will come of telling her. I need to put my feelings aside so I can be a good friend to her right now. How can I do this?