i think it might be tidus

im not what they say i am cuz they want some relief(they say hes just poisoned from sin, but hes not
i did what they say i did but against my choice(kill sin, i think, i nvr finished game)
he should be mine but he would be new (jecht is his father but since hes sin, even though hes jecht hes not really jecht(as in how tidus remembers him.
the happiness i had is gone forever(zanarkand is no more)

hints
related to sin(hes sin's son,sin is jecht)
in the riddle to of the they's will be changed to a pronoun