Luis died of AIDS. Rather, he died of everything else that accompanies it. His body gave up the fight and his heart simply stopped beating. He was well cared for by the doctors at Cabrini hospital, but for Luis it was too late.
It is said that no one dies of AIDS any more in the US, and that is true for most people. For it to have been true for Luis it would have involved more soul-searching than it was possible for him to do. It would have involved admitting to himself who he really was, and then admitting that it was possible for him to become ill. Strangely enough in this day and time and place (New York City), when there is barely a stigma attached to being gay, it is still not possible for everyone to "come out".
From the time Luis first went into the hospital to the time his body gave up was a matter of weeks.
AIDS wasn't all that killed him. Luis died a victim of Latin machismo. Luis and his three brothers were raised to believe that all that mattered was a strong body. Education and intellectual pursuits were meaningless. Luis didn't fit into that. He was the "other", and so became close to his mother, and missed her greatly when she died.
That also, I believe, is why he chose the Anglicized version of his name and preferred to be known as "Louie", even in print. That was his small way of rejecting machismo.
Still, he tried in his own way to show that he too could be a "real man". He learned a little carpentry and built a closet system in his house that was superior to anything his father had done (his father is a contractor and handyman). His father was not impressed. Takes more than building a closet to be a real man, you see?
In "Boyz in the Hood" the protagonist tells his son "anyone can have a child but it takes a real man to be a father".
When Luis first was hospitalized, his father had just left for Colombia. His father was notified at his second hospitalization that Luis was in very poor shape and may not last.
Luis died waiting for his father.