I'm having trouble picking up a girl's signals.?

I have a crush on my bestfriend's girlfriend. Her and I "hung out" last night but it felt mostly like a date to me. When my bestfriend and his girlfriend are together they hardly touch each other. I don't know if they're trying to be nice (knowing how much I like her) or if they are always just that way. Also, when all three of us are together or in a larger group, she spends so much time with me I'd like to think of her as my girlfriend. We can stare at each other and have those comfortable silences. I want her as my girlfriend but I don't want to piss off my bestfriend, and I'm kind of doubtful she feels the same way for me. Should I avoid her completely? Should I tell her how I feel?