Light didn't win that day. Rem had fooled the teen for Misa's sake and knew that the only way for her to be truly safe, Light had to be caught by L. And so, at the last second, she wrote another's name and L lived after figuring out Light was Kira.
Instead of being sent to death row after conviction, Light knew he was fucked when he was sent to an isolated ward in the maximum security prison for the criminally insane for the rest of his life. At first the white padded room was bearable but the genius youth could feel that with time, the lack of stimulation wore on his mind. Eventually after putting up a good fight, Light went insane and hallucinated things constantly, such as a world where he won and the male occasionally engaged in self harm.
L, after growing concerned, felt pity for the person who was his first friend and allowed him a therapist (against his better judgment). It was you. At first, Light had been apprehensive about you but now - you were his world. His balm that soothed the nightmares and hallucinations. His saviour. Maybe his God. In his mind, you were solely his just as he was yours.