I really like this girl and she likes me too, but she likes being single. How do I get her to be with me?

Her and I have liked each other for the past three years and she finally admits to liking me the other day. But she likes being single. I have tried doing everything for her. I have bought her things, said the nicest things to her and done things for her even when she is being a bitch to me. What do I do to get her to want to be with me?
I really like this girl and she likes me too, but she likes being single. How do I get her to be with me?
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