In matters of love and loss, it could be argued, the principle of equivalent exchange did not exist.
The first time, when the Gate had devoured his mind and body and soul, treating every scrap of his young life merely as dues to paid on an overcharged cosmic account, his brother had been there for him and had managed—against all odds, against his own fear and pain—to reclaim at least the most important piece of him, using his own flesh and blood to bargain with a cruel mockery of a just divinity, and, despite the guilt and horror that had clamped down on Edward's heart as a result of affixing his little brother's immortal soul to an unfeeling hollow metal shell of armor, Alphonse had been overwhelmingly grateful to simply have survived that terrible transmutation and not have been utterly consumed by the blackness that lay within the Gate.
The first time, his brother had been there for him, and Edward's desperate gamble had been his salvation, the light of his world.
The second time... Ah, how the second time had mirrored the first, reflecting it back in a warped, nightmarish way: the brothers standing at the outside curve of main design etched into the floor of the abandoned church—the elder determined and reckless, the younger hesitating, his methodical mind turning over their working theory over and over as he was nagged by the sense that he was missing something, something wasn't right, and he had to figure out what it was or this time...this time, something even worse might happen—and once again the dead occupied the center of the array, though...
Envy had shrieked endlessly, letting out streams of violent, vitriolic curses. His slender body had arched up in furious spasms as he fought against the power of the arrays drawn on his pale flesh, marking the insides of his wrists, between his collarbones, his abdomen, his ankles...marking, and binding—a variation on the sealing array that Ed had seen on the floor at Dante's, reworked several times by the young genius for this expressed purpose.
The first time, Ed had asserted by way of explanation, partly starting his rational aloud for his brother and partly in answer to Envy's howling outrage, they'd traded the necessary elements that compose an average adult human, all of Al's young body, and most of his own leg, and in return they had managed to created something that was not only not human, but not even properly a homunculus either, as it had still needed the red stone to make order out of the chaos of its flesh.
This time... The alchemist had clapped his hands in emphasis and had marked the floor with the complex array. They'd start with a completed homunculus, one who had all those hundreds of stolen human lives fueling its body like a powerful, simple alchemical battery...like the Philosopher's Stone in its most primitive form...and they'd work backward, first giving to the Gate, and then taking.
Envy in exchange for Al's body. Neat. Clean. Fair.
Ed had stood back for a moment, examining his work with a critical eye, then had burst out one of his broad sunshine grins. This would work, he was sure, and even if it didn't—though he sniffed softly when Al questioned him about possible failure—they'd at least sacrifice the troublesome, violent, hate-filled homunculus to the Gate and then bring the quickest ending they could to the transmutation by burning off the energy released somehow...he'd figure that out as he had to...and leave Al's body untouched in the Gate for later recovery.
And if it did work...
Ed's golden eyes had shone with passionate excitement as he turned to Al, and the younger had marveled that his brother could be so confident even with the memory of what had happened on their first attempt at human transmutation bolted into his flesh and bone—he'd been cocky then, too, and it turned out that there was more in heaven and earth than Edward Elric had included in his formulas and theory-strings, and that error had nearly cost them both their lives—but Ed's zeal had been infectious and despite Al's misgivings he had to admit that everything seemed flawless...
"We could get everything back again, Al," Ed had whispered, his softly awed words cutting over Envy's caterwauling easily in the stagnant air, and he had clapped his hands again and knelt down in something almost like reverence before the array.
When his white gloved fingers had touched down on the floor, the world exploded.
The second time, when the Gate had reached out with greedy, grasping hands and latched onto one who dared challenge it once again—the one who had not yet learned that there was no tricking those all-seeing eyes and that the demons of the dark knew all the deceptions deep within the human heart—he had been completely unable to call back to him that which he loved most in all this world, his fingers clawing frantically at sucking air, incapable of finding purchase in the fabric of the cosmos, and his screams had meant nothing, nothing at all...
In the wake of the Elric brothers' second attempt, it was Alphonse's deepest, most profound sorrow and regret that in matters of love and loss the principle of equivalent exchange was not applicable, and he had not been allowed to repaid the debt he owed his brother; he had been unable to save his Edward as Ed had done years past for him.
The Gate had swung shut, his beloved had been lost, and that way was closed to him.