Tldr: I did everything right, but she still went home with another guy. What happened?

I initiated everything. Perfect kino. Perfect rapport. We were making out and then the the guy who I knew was taking her did. Heartbreaking in a way but I want to know what went wrong. Preselection on point. Status..had everyone associated. Still lost her. What the fuck went wrong?! I wish I nailed it first try.