Does this make me a bad friend?

Tabby

I've been crushing and lusting over this boy for the last two years (on and off) but the problem is that he's my best friends brother. I've never tried it on with him out of respect for my best friend but when ever I go over to her house all I can think about is doing him. Am I a bad friend? I told her that I used to like him and she said she was fine with it but I feel like she just said that to not hurt my feelings.