It was a possessive love, always a possessive, almost selfish love that drove him. It had driven him to kill on the behalf of his dead mother, ironically, it had driven him to kill to preserve the life of his wife, only to kill her himself. And now it drove him after his son, his blue eyed son who would choose death over a life with his father.
Like her.
But no, Padme had not chosen death, he had forced it upon her. In his dreams, their faces merged; Padme, with her hands clasping her throat pleading in her eyes, shaking her head in denial, Luke, clinging one-handed to life over a great chasm, eyes pleading, shaking his head in denial. Then Padme falling, collapsing to the ground, Luke falling, farther and farther while the light inside him screamed in agony.
His fist clenched, an old need rearing it's head, a need for attachment, for human contact, and, although he would die rather than admit it, a need for love. A need that had focused itself upon his son, and now drove him across the galaxy, plowing through stars and bridge officers alike, to finally find him, only to be rejected. He remembered the rush, the surge of emotion as he had first caught sight of him, his pride, how he had searched the boy's face, claiming bits of his own and bits for Padme. And then he had watched him fall. And since then, the horror of that moment had been nagging at him. And a little voice whispered from it's quiet stone cage of his heart; can you stand to watch him fall again?
The wound on his arm tingled, and Vader turned to look a it, at the pale, sickly flesh above the wires of the replacement, a deep, jagged gash still oozed blood. Vader stared at it, transfixed, lifting one hand to pull the half-healed edges back away from each other, the pain echoing dully and fading from his pain-racked body, inconsequential, one of many. More blood oozed from the cut, Vader watched it smear on his black fingers, rubbed it against the papery skin of his arm, vibrant red against the sickly white. Life and death. And he bled, just to know he was human. Far away on a dusty Tatooine night, Luke Skywalker caught the flesh of his arm against the doorframe of Ben's house, cursing softly as it spilled slowly across his arm.