When she complains about her boyfriend. Makes him look bad in your eyes. Acting like a victim so you can feel pitty for her and make her happy(its not your job to make her happy but her BF so be carefull dont fall for it).
When she talks about herself in sexual way and apreciates your manly body with hints, touches and looks(when she looks at muscles or croch). When she gave up time with her BF in order to be with you.
When shes chilled out with her BF but excited with you. When shes real carefull listening what you are saying. Shes serious about your attention.
Doubt kills more dreams than failure ever will