Because people have made her promises in the past and they've broken them. Because no matter how hard she works or how good of a person she is, she doesn't believe she is worthy of love. Because she’s had too many people leave her – both intentionally and unintentionally – and she doesn't want to give you the chance to leave too. There are a million reasons she might not be able to believe that you love her. And there will be a million more in the future.
She’s been through so much. So much. She’s had moments where she didn't know how she was going to keep going. Moments where she didn't think she could get out of bed, and worse moments where she did get out of bed and she felt like an empty shell while she was walking around. At some points, she was so lost and so torn up that she wasn't even sure if she was real.
Sometimes she can’t believe that you love her, but other times she doesn't want to believe that you love her, because that would just be too good, and good is not what she’s used to. She doesn't want to love you and then lose you. She’s scared, because having someone and then not suddenly not having them is a lot scarier than being alone.
She might be extremely secure with herself, or she might think she is nothing. She might be somewhere right down the middle. Regardless, she can’t believe she will find love with someone like you, because she hasn't seen enough of it yet. She’s seen some beautiful love, but she has a hard time remembering that kind of love when she’s watching the sadder stories unfold. She’s seen her friends get hurt, and she’s seen her friends hurt other people. She knows that breaking someone’s heart doesn't always mean you’re a jerk or a heartless monster. She knows good people hurt other good people. Sometimes one person just doesn't love another in the same way. Sometimes they did love that person and then they fall out of it. Either way, they have to be honest with themselves, and they have to be fair to the other person. In the end, someone always gets crushed.
Maybe she’s afraid to love you because she’s been the person that’s broken someone else’s heart. Being hurt doesn't always have to mean you were on the receiving end. You can hurt yourself by hurting someone else, to the point where you can’t even breathe and you hate waking up in your own body, knowing what you did and how you made someone else feel. Maybe she loved someone but knew they weren't the right person for her, so she had to leave them. And now she’s worried that you’re going to do the same thing to her. That, even though you love her and you are kindhearted and you have the purest intentions, you still might have to walk away. She knows there are so many reasons why this might not work, so instead of paying attention to the one reason why it will, she focuses on the ways it won’t. It’s called self-preservation, and it’s all she knows.
She listens to love songs and she lets them pass through her and she wants them to be her life. But she can’t. She wants to be that sickeningly happy. To be so in love that you laugh at things that aren't that funny and so in love that you aren't fazed by rude people or stressful situations. But she won’t let herself give into the fantasy of leaning her head against the train window and listening to that song and wearing a dizzying smile as she thinks about you. She’d rather stay on the cautious side. This side of things is not thrilling or exhilarating. You don’t get goosebumps, and you don’t feel as if you need to go outside and run a mile in order to get rid of the boundless energy you feel just from thinking about someone else. This side isn't living. But it’s safe and secure and she has a grip on her head and her heart. She doesn't feel shaky or unstable. She’s in control.
Maybe, technically, she does believe that you love her. Somewhere inside of her, once you get past all of the defense mechanisms, she is soft and she feels things and she believes that you love her. But this is also the part of her that is the most vulnerable. She knows that if she’s going to let herself feel what you’re telling her and if she’s going to believe that you love her, she’s going to have to expose her soft side, her vulnerable side – the side she works the hardest to keep safe.
She wants to trust you. She wants to believe that you’re different. She wants to give you the chance to break her into a million pieces. But you've got to meet her halfway. You've got to let her know that you’re scared too. You've got to remind her that you’re just as much at risk, because she can break you into a million pieces too. If she can’t believe that you love her, tell her anyway. Every day. Show her. Make her understand that you’re not going anywhere. Because at the end of the day, you want her to be staring out that train window, thinking only of you.