And when time is reversed, no one will ever know how much Ianto Jones sacrificed to ensure nightingale's success.

This is so sad but heroic, Ianto Jones' voice is both his salvation and his curse - it saves him from the Toclafane, but changes him so completely that he ceases to be who he was and instead becomes something of legend, something I suspect he never wanted to be. The threat of the Toclafane left him no choice though, he's Torchwood, it's his job to protect Cardiff and the earth itself, and he'll carry out his duties no matter the personal cost. He lends his support to Martha, without her having the faintest idea that he's even there, following along behind her.