Is it ok to date her my sisters (bff)?

she's my sisters best friend, and she's practically been living wiht us for 8yrs, she's wicked rich and her parents never home always with the ppl that work in her house so she spent a lot time with us and my mom treated her like one of her children she even went to her pta meetings and she's in our family album and went on every family trip with us, but back to the point last summer my sister was out and me and her was home she came to my room while i was watching a movie she said it was cold so we kinda cuddled and that point we almost kissed but i backed, but couple days ago she told me how she felt about me i'm attracted to her but i kinda feel lie she's one of my own sisters i love her to death, so will it be wrong to date her if not how can i get the image of her as my sister off