This is far more than a poem. Generally, no rhythm and no rhyme bother me. But, here, it flows so nicely without them. There is no need for capitalization; the mind doesn't speak in sentences.
This very accurately describes grief upon losing someone you really care about. The internal rhyme "pain" and "name" is so perfect! I know the exact feeling. The repetition of the one month turning into two etc. really hits the point home. The years pass, but the pain doesn't.
The last lines were chillers. "little brother, where are you? come back please" How meaningful these words are!
Overall, the words in these poem really make an impact. I can feel your emptiness inside as I read, and I know what you are feeling. And I sympathize, though I do not even know this person you speak of.
Fantastic job. Keep writing!