This is how you lose her when she wanted to be yours.

You lose her when you stop paying attention to her. To her feelings. To the changes in her behavior. To the sadness in her eyes. To the things she's been subtly asking you to do but you've been oblivious to them all. 

You lose her when you give her the feeling that her presence in your life is not important. That you're find without her, that you don't need her in your life as much as she needs you. When you make her feel that spending time with her is an obligation and not something that will make your day better.