I've been pretty much best friends with a girl for over 5 years, and there has always been chemistry and tension between us. We tried dating once but she backed out because of her own stated commitment issues and life circumstances.
I'm the closest thing she's ever had to a boyfriend and the only guy to ever even take her on a date which is crazy because shes very traditionally attractive and could have any guy.
We hang out 1-on-1 constantly, travel to motor races together, stay in hotels, and have slept in the same bed platonically many times. She tells me I'm very attractive and a great guy, is very flirty with me, we know everything about each other, her friends and family even say we should date, and when anyone has asked her for reasons why she wouldn't, she said she couldn't think of one.
She even made a marriage pact with me (her idea) and wants to come to my work Christmas party saying we could joke that we aren't "dating" but getting married in 8 years. She once called me while drunk and said I'm the only guy she's ever felt really cared about her and that I might be the only guy she's actually loved. But whenever I talk to or date other girls, she acts like she doesn't care and just says she knows I'll "find someone," which hurts because I want it to be her.
The worst part is that she completely deflects and shuts down any time I try to have a serious talk about us. We're also core members of our friend group so I'm scared of ruining things – but the limbo is draining me. How would you recommend I approach this?
TL;DR there's clearly romantic tension between me and my best friend but she shuts down whenever I bring it up. How do I approach this?