Falling for a friend, hor to approach her?

I have a friend I've known for about 3 years. she's become one of my closer friends and is one of the few people I fully trust. I've always had some interest in her but never had a chance to make a move (she's had a boyfriend basically since I met her). Well as of a few week ago, she is now single. As pathetic as it sounds, I have no idea what to do. Do I just ask her out? Do I just tell her flat out how I feel about her? I feel like I have no idea how to approach her about it or how to even start such a conversation.