My sister would be the absolute perfect girlfriend.

My sister (22) and I (20m) have become very close since I left HS. My friends tell me that they can’t imagine having a relationship as good as the one we have. She would be the absolute perfect girlfriend. She’s the only person I’ve ever met that I really connect with. What am I supposed to do? I’ve never had a real relationship. I’ve had sex with 4 people but never had a relationship. I really wish she was my girlfriend. Just imagine the perfect girlfriend. She’s that but I’ve been taught this is wrong. What am I supposed to do? Can someone show me a way out of this? I don’t want to be lonely. I hate my life.