Dating My Best Friend's Brother...

I really need advice. I've been best friends with this guy for about five/six years. Over that time, we both had feelings for each other but circumstances never worked out in our favor and we never even talked about the idea of dating because of it, but the chemistry was undeniable. About half way through my friendship with him, I befriended his little sister and we became best friends. We spent every day together. Within the past year, the brother and I admitted to having feelings for each other. Our parents and everyone was totally supportive, and he even moved in with me right away. He makes me so happy, I love him, and I see a serious future with him. The only problem is, my best friend has basically turned her back on me. She even says she doesn't want me at their house when we all return home for holidays, and she doesn't want me to attend her other siblings' weddings which I am invited to. My boyfriend's parents see what's going on and they don't judge me or hold anything against me, they have been nothing but kind from the start. I have tried talking to my best friend and feel j have bent over backwards trying to accommodate her as much as I can without sacrificing my own happiness. (our friendship had the dynamic where I give, she takes. Maybe she sees it differently.) Anyways, she accepted us at first and even lived with us for a few months, but as soon as it came time for me to be around her family, she acts like she hates me. Please tell me she is being unreasonable! I understand it will take time to adjust, and I would understand if her brother and I weren't a good fit, but we are so happy together. I'm trying to fix our friendship, but she doesn't want to fix it. :( I feel horrible.