I'm in love with my best friend?

I really can't believe I'm posting on one of thse sites but I've been love with my best friend for about 6 months now. We have been best friends for about 2 years and tell eachother everything, talk every single day, all day, and hangout all the time. I've always had some feelings for her but after girls upon girls that just weren't working for me, I developed some serious feelings for her. I thought I was just crushing but it became painfully obvious that she was the one. There is one major problem. Her ex-boyfriend of 4 years has been one of my closest friends for 5 years. They broke up a few months ago. They still hangout and get touch and cuddle when I'm there too, which is painful for me to watch but I act like it doesn't phaze me. But it's obvious they aren't right for eachother and she knows it. Recently her and I talked about what we meant to eachother and she told me she cared about me more than anyone amongst some other things. But since that talk, things have just been weird between us. I don't want to tell her how I feel at the risk of causing turmoil between me and my close friend of 5 years, but at the same time this is eating me up and feel like I can't go much longer without telling her. Is it normal to be in love with my best friend? I need advice, hopefully from someone who's been through this but I'll consider anyone's thoughts.