Help Developed feelings for my bestfriend, how do i get rid of it?

There is this girl i have been friends with since the summer. Eversince then we have been bestfriends. She's smart, cute, and a great personality. I have never had a problem seeing her as just my best friend but all that changed lately.

Recently she had gotten sick really bad and it tored me up inside to see her so sick and in so much pain. I did alot to help her like get meds for her and cared alot for her. From the day i saw her sick, i began to really care alot for her even more than a best friend should. I began to think of her in a romantic manner. but the problem is she has a boyfriend that is also a friend of mine i made over the summer. We hang out alot almost everyday the three of us.

Until recently when i began to develope feelings for her, i couldn't stand seeing them close together when we all hang out. I know she really cares for me because we share alot of stuff with each other, we text and talk alot.
Recently i tried to be distant with her to try and remove these feelings. but she would get depress because i didn't talk to her or reply to any of her texts. she would text "i miss you", "why are you not talking to me", "have i done soemthing wrong" etc. I couldn't let her feel sad because of me so i replied back and told her that when she was sick i began to cared for her more than i should have as a friend. that i don't know what to do and the only way i could think of is to be distant with her and hope these feeligns would go away.

She asked me never to leave her alone, that she doesn't want me to do that. That the first thing she thinks of is me when she is in trouble. that a day doesn't go by when she doesn't think of me making her laugh and etc.

There was this one day where i tried to not look at her much and talk to her when we were around friends. She would text me that night saying she was really hurt that i would act normal around others but ignore her when she was talking. that it hurts her alot that i did that to her that day.

What am i suppose to do? If she didn't had a boyfriend i would so ask her out. But i can't beause she do have a boyfriend, she cares alot for him. And even if they broke up i can't ask her out anyway. And i see them everyday and i feel so hurt and depress when i see her with him. I'm a horrible friend to her boyfriend for feeling this way towards his girl, and i'm horrible for doing all this to her because she cares for me. I'm so confuse and i'm suffering everyday when i see her. I can't remember a time when i don't have this sick feeling in my stomach and this empty hole in my heart that i can actually feel.

what do i do? I'm sorry for the long story.