Falling for a girl whose best friend likes me

I have started falling in love with a friend who I have known for a about a year. We get on very well, but I have no clue how she feels about me. The trouble is that one of my best girl friends, who has liked me for over 2 years, is also best friends with the girl I am falling for. I'm pretty confident that the girl I like wouldn't do anything until the other girl has moved on, but when I told the girl (who likes me) about everything, she got quite upset and said 'that she isn't going to get over me just for me - that would be unfair on her.' The girl I like knows nothing, and I'm not sure if I should tell her how I feel, as she wouldn't want to do anything while the other girl still likes me, and then our friendship would get fairly awkward.