how can I get her friendship back?

[William]

Words cannot describe how much I care about this girl. Having her in my life is the best thing ever. Whatever I do, wherever I am shes always on my mind and in my heart and I really do love her. I messed up. I told her how I felt over a facebook message and she didn't deserve that. I hate myself for it. Ever since then ive been in a depression for months. I can't believe I've messed up on something so very important to me. She blocked me on facebook and hasn't talked to me for months. And it hurts so much. I was going to tell her how I felt about her in person becauae she deserves that but a senior asked her out to prom and she said yes. My heart just shattered. It hurts seeing them together. But I've heard things about this guy and the way his relationships end and I can't let her face that alone. I want to get her friendship back. I want to try and make her see the benefits of our friendship than trying to focus on the past. Whats the best way to get her friendship back?