Why is my crush nervous to approach me?

I have a crush on this girl. We're really close friends for over a year now. As time went on, I developed feelings for her. I don't know how but I did. So it is almost always me who initiates the conversation but when I do, she seems very enthusiastic and the conversation usually lasts a long time (depending on the available time). But on the other hand, she doesn't really go to me to initiate conversations. She isn't afraid to ask her friends things and openly approaches them but she kinda is nervous to ask me questions but as I said, she's enthusiastic when I talk to her first. I really wonder why she treats me that way and different from her other friends.
Why is my crush nervous to approach me?
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