Full spoilers follow. The film's architecture is a slow convergence toward a single moment on the boulevard. Throughout, Luke's addiction is the withheld information — the thing that explains his absences, his volatility and his refusal to let Hasley fully in, and the reason his relationship with his father (Luis Zahera) is so corrosive.
The ending. Luke walks toward Hasley carrying a rose. A truck appears; he runs to save her from it. The screen cuts to black, and what we see next is the rose lying on the ground while an ambulance siren sounds somewhere in the distance. Luke has been hit, and he dies.
The time jump and the letter. The film then leaps forward. Hasley is at the boulevard reading a letter Luke wrote before his death; his voice narrates it while we watch his funeral and follow her grief at home and at school. In the letter he reveals what he could never say aloud: that he had decided to enter a rehabilitation centre for a year to overcome his addiction and his pain.
What the letter retroactively explains. This recasts the final act entirely. Luke's withdrawal, his distance and his apparent pulling-away from Hasley were not rejection but preparation for leaving — an act of self-preservation he intended as an act of love. The rose becomes a goodbye as much as a courtship gesture. The tragedy is therefore doubled: he dies not at the bottom of his addiction but at the exact moment he had chosen to climb out of it, and Hasley learns the truth only when he can no longer be part of it.
The real ending is Hasley's. By giving the closing movement to her mourning rather than to his death, the film resolves as a coming-of-age: the boulevard, once the place where the relationship happened, becomes the place where she reads, grieves and continues. What Luke leaves her is not a future together but the proof that he had wanted one.