Captain Jack Sparrow doesn't know why it hurts so much to see the whelp get stabbed. He doesn't really like him – doesn't even really know that much about him, other than the fact that he has a very large need to be courageous and noble and that he, somehow, manages to uphold a sort of hero complex that Jack's never been able to put up with. Plus, the kid's got this whole attraction to distressing damsels, and really, Jack never should've helped him those years ago, because look what he's gotten the boy into!
Elizabeth is shouting something and she's crying and Jack just sort of stands there, feeling about as useless and low-down as Jones should be feeling. His heart lurches and he nearly drops the knife in his hand, and his tongue sort of shrivels in his mouth like he's tasted something bitter. Elizabeth is screaming more now, and she's leaning over him, and Jones looks crueler and crueler as seconds pass, and Bootstrap lunges at him with fury and Jack's still standing there, and the more he thinks do something do something do something, the less he feels like he can actually move, because the little eunuch has somehow latched himself onto Jack's heart, and it's a feat that no one else has really accomplished before.
Jones is winning the fight against Bootstrap, and Jack sort of snaps himself out of it when he hears Elizabeth's screams and he wonders why he ever thought he could take her from Will and just thinking about it makes him feel like the world's biggest piece of scum. He knows he has to set it right, has to do something to save the boy – because really that's all Will is – and he doesn't think of it right away, because for a moment, he forgot that he was literally holding Jones' heart in his hands.
So he restrains himself from stabbing the heart, and he bends down towards the boy, puts the heart next to him, forms a fist with the boys hand, and holds it as he forces the knife into Jones' heart, and he can't help wondering why he's giving up immortality for someone who he hates, just so the boy could be with his murderess.
And maybe, that was Jack's hero complex.
AN: So, just a little quickie oneshot/drabble thing that I did in literally fifteen minutes. I've been thinking a lot about DMC and why Jack would give up immortality for Will, so I thought, why the hell not!