We fell in love with the same woman. Help!

I have a girl best friend for 5 years and I have been loving her secretly since then. She was sweet to me and I know she only did that because I AM HER BEST FRIEND. I was so stupid to misunderstand it as something else. It was late when I realized I already fell for her. My mom likes her very much. Shes already close to my entire family too. Everything is fine with me as long as she is there for me. For 5 years that we have been best friends, I have never seen her loving somebody else. I took it as a sign that she likes me too. However, I cannot tell her how I feel because of someone; I value our friendship and most of all, because of someone very close to me-- my brother. Just a week ago, my younger brother told me he loved my best friend. He even asked me to help him out. I was broken when I heard it. I had a lead that he likes her. I just thought it was nothing. Since I was young, I used to sacrifice what I want for my little brother. I love him that much but things are different this way. I love my brother but I love my best friend too. I love them both and I was puzzled as to what to do with this. Should I sacrifice my love for my best friend and help my brother or ignore my brother and tell my best friend what I truly feel instead? Does the latter make me a bad brother? Help!