I've watched some motivational video saying that it's not to send letters to ourselves although it may seems weird. You should love yourself first no matter what :)
Mira,
It's okay.
Give time to yourself. You just happen to like him so much but that doesn't give you the right to being hard on yourself. It was something that you can't control. You fall for him, yes. He suddenly trapped inside your heart, yes. He refused to leave your mind, yes. But that's just it. Let the feeling there because someday it will go away and dissolve. You will eventually stop feel...ing it. The harder you push yourself, the deeper your feelings for him, the more you will like him and the bigger painful heart you will receive. Stop torturing yourself. You didn't deserve to feel this way. What have you done to other people until you face all this? No. Don't blame God and destiny. This is one of your learning process and trust me you will become stronger with the more pain you've experienced. But still, don't you ever starting to hate him just to switch your feeling. Hate won't resolve things. Plus, there's a huge percentage that instead of liking him, you will slowly love him and when you love someone, his effect on you will get extremely bigger. That time, you need more than courage and strong heart to handle it. He wasn't at fault at all in the first place. He can't control your feeling for him, he can't control his feeling for you. Perhaps he got some other good and better choice but don't feel down, you can always have better option and choice than him either. Open your heart and let it show you the way, invite the right person in. Yes, the right person will come in and if its still him, isn't cute? if its not him, trust me that person will be better than him.
YOU DESERVE TO BE LOVE!
And you will receive one. I know you are wonderful person, beautiful, cute and funny. Who doesn't like to have someone like you?
Keep your head up and put smile on your face. You are HAPPY!