Dear Zack, 
I know you really don't like me right now, and even though I don't completely understand why, I need to write you this. 
You need to understand why I was upset. Yes upset, not mad. I was never mad.  Look at our past 4 months together. You haven't  gotten me a single present for any holiday, even though I got you one for every one. And I know you said you said happy birthday, but if what you said is true and it's Issac's fault I didn't hear you, I'm sorry for that. But maybe you should have said it again later.. 
I don't know why you're so mad at me, but I guess I could understand some reasons. Meghan and Dillen told me you're happier now without me, and I'm glad. I just want you to be happy. So if that means that you don't want to be with me anymore, I can deal with that. But tell me. Not in capital letters and swearing, but nicely, please.. 
And before you make up your mind, think about all our memories together. Halloween. Mr. Nick's class. My basement. Your bedroom. The movies. Can you really move on without looking back after all that? I know I can't. The past 2 days I've cried myself to sleep and woken up feeling totally empty. 
I love you. Even through all of this, all your angry messages, I can feel your... voice coming through them and it makes me miss you so much. 
Please, please just think about the times when you used to love me. Do you really want to lose all of that over this little thing? 
I'm sorry for causing you so much irritation and trouble. I don't mean to. It's just the way I thought I had to get your attention.. But I was wrong. 
I really do love you. And I miss you, so much. 
If this didn't change your mind and you still want to break up with me, I'm okay with that, as long as you're happy. But just know that I'll always be here.. 
Sincerely,
Sarah