In my experience, I was absolutely miserable for many years until I very nervously asked if I could be "more than just friends" with a certain girl on whom I had long-time crush. She kindly declined on account of already being in a relationship unbeknown to me. Well that made me REALLY miserable, closer to suicidal. And so, during my deepest, darkest, dismal depth of despair, I finally realized that if I am to have any chance at getting a girlfriend, I would need to change. I would need to stop beating myself up, physically and emotionally. I would need to improve my level of self esteem, if not for her, then for any future potential mates. I am glad she rejected me because that is just the motivation I needed to improve. If she had accepted me as I was in my depressed state, our relationship would probably have been short lived, and I would still be depriving myself of all positive emotions to this day.
So if you want your life to be less of a bummer, ask her out and hope she rejects you. You need to feel confident about yourself before you can feel confident about a potential relationship. If she accepts you, well... give it a try, I guess.