Why do you look so familiar ? (слэш)

What if Harry Potter had never been to Gryffindor but to Slytherin ? What if he had accepted Draco’s friendship , what would it have changed ?
What was this familiar feeling ? And were these fragments of the past, like distant memories, real? Why did the sight of these people make him so melancholic? And who was this blond who caused a gentle warmth in the depths of his being ?
or
A master of death Harry fanfic but this one does not remember, at least for now.