How can i stay friends with someone I'm in love with, but they can't return the feelings?

I am a who fell for my best friend (who is straight), about 3 years ago. We've been best friends for about 7 years. She knows I'm gay. I have never told her how I feel, although I know she knows, because it is very obvious and she has made comments about me wanting her as my girlfriend, jokingly. We are very close, i'm like a sister to her and have helped her through some very hard times. I want to keep her in my life, but sometimes it is unbearable and I get really depressed. How can I deal with this? Also, when we drink.. she flirts w/ me, has given me hickey's, we've made out once, we spoon sometimes, but I have NEVER been the one to initiate it. Ironically, I am the one to stop it cuz I know she wouldn't do these things sober. I'm just all messed up and going crazy now and on the verge of saying I can't just be your friend anymore and end the friendship. But if I could get rid of the feelings somehow, or learn to deal w/ them, I would much rather be bff. Any advice?