Is it possible to live as a friend with a girl whom you like?

I like her but I never told her because she already has boyfriend. It was big mistake from my part that I kept talking with her and now she considers me a very good friend and I am irreplaceable part of her life, as per her. If I think about myself, I am feeling like a sucker who can't move on. I still wait for her replies even though I know, she will never ever be mine. I tried avoiding her for few days and she messaged me so many times asking where I am and what happened to me. Seriously I felt like I am trapped now. I can't confess anything. I am also unable to distance myself from her due to this friendship thing. I am unable to move on. Is it possible to keep this feeling always like this or I can overcome my feelings and finally consider her just as a friend. Has anyone ever tried this? Does this work?