<em>I think this is somewhat hard to correct, because it is creative writing and it is written in a very personal way. Normally in formal writing, you must have a noun AND a verb or you have a sentence fragment. In creative writing that is not always the case.</em><em></em>

Memories of yesterday.

Yesterday, I thought you were the only one. The definitive. That you were for me. (<em>For me, it would read better if you said:  Yesterday, I thought you were the only one, the definitive. That you were for me, and I, for you.) </em> And me, for you. I would guard you until the end. That <em>You</em> would not hurt me and  <em>or</em> would not let me ever want. Because being <em>Always </em>together, hearts beating as one. Because what we felt for each other had no name, was indescribable. <em>(Or:  What we felt for each other was nameless, indescribable.)</em>

Today, I feel cheated. I can hardly believe it. I can see how you've changed. You're <em>Or:  (You are not for me.) </em>not for me. I am not for you. I missed your affection when I've needed <em>it</em>. Did not you care it deserved <em>(Could be either: Did you not care that I deserved it? or: Didn't you care I deserved it?)</em>. I've been the one who has been (maybe say: who was honest) honest. I felt heart. <em>brokenhearted (or heartbroken).</em> But for you, it was all a game. A rather macabre game.

What hurts today, tomorrow will make me stronger. <em>(I suggest the last sentence start with the word "Tomorrow". With the three paragraphs starting with Yesterday, then Today, then Tomorrow, it makes it a much more powerful statement)</em>

I would not correct this. The highest level of communication is emotion.  You expressed your emotion so well it is still remains even in a different language.   Corrections are for everyday functional language and tests.