I'm looking for this manga I read some time ago, but I don't remember anything about the main story.

What I remember is the past of one of main characters (it could be the main love interest, not sure) from when he was a child.

The boy, before he was born or when he was very little, had a bother that died and that affected their mother a lot. So without no one realising, the mother started treating the boy like if he was the dead brother. It's like the mother is living again the life with her child.
That's until the boy reaches the age when his brother died. The boy goes to show his new uniform (of high school or middle school, I think....) to his mother, but because the brother didn't get to wear the uniform the mother begins acting strange like she doesn't recognise who the boy is.
All the time she believed the boy was the dead brother so she wasn't aware she had another child. That affects the boy a lot.

That's all I remember.
As for the genres it could be a shojo or even a yaoi.

Sounds like Global Garden but there is romance in it :/

Sounds Like Loveless a little but not exactly... either way, you should check it out!!

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`~Yo~`

It's Yume no Kodomo! Thank you very much for your help!!