If the youthful Death Eater had thought his heart had first cracked the day she had chosen James Potter, had thought it had cracked further the day she had gotten married to him and had finally cracked beyond repair when he had learned about his first love being with child and then giving birth to James Potter's son, he was quite sure that it must be broken at that point.
Severus Snape was the kind of person who didn't usually show his emotions or basically anything else internal very easily. While he regretted once having joined the Dark Lord and a lot of what he had had to do merely to keep in His favor and later under cover, fulfilling the bastard's wishes, and many other deeds – some nothing less but gruesome – in his life he most regretted the way everything had changed and how it had eventually gone between him and Lily. The worst which he had ever had to do in his whole life was finding her motionless… her smile lost upon her lips forever and shimmers never to be seen in those intense pools of olive green anymore, all having died together with her… residing in a world where he couldn't even see her with another anymore.
He had been there first… had been the first to set foot into the house of the Potters, to confirm that the first burning and then oddly cooling sensation across his Dark Mark, which he and many others of his fellow Death Eaters had felt, might indeed have meant that what they all had feared and some of them maybe hoped for deep inside – Severus being one of the latter. The youthful Death Eater had dared with risk of his life to set foot there, not knowing what had happened or what he would find there… It had touched him minimally to step over the lifeless body of James Potter, but from the moment Severus had passed him like that, his heart had sunk and had constricted painfully, his hopes for finding Lily and her son if necessary alive and unharmed decreasing with every breath spilled from his lips. His breaths had come faster, just like his hopes had melted… faster with every step, intuition guiding. With every step further, the screams of her son had gotten louder, the absence of her soothing voice while cooing over him… deafening.
Severus could feel his pulse beat against the side of his head as he made his way over to the first landing, light from one of the rooms pouring onto it and enabling him to see well without having to use his wand, his fingers clutched about it tightly nonetheless, just in case that… Something told him that his Master was already long gone, though… whatever definition 'gone' could take on right then. He had obviously been there.
James Potter had died defending the family he had never had, yet had so much wanted. If Lily and he… then he most likely never would have fallen in the embrace of the Dark Lord instead.
He never could have readied himself for the sight of his first love lying there motionless, her beautiful olive green eyes gazing into nothingness… His breath was expelled in one second, and he found himself struggling for air… remaining upright…
Tears burned in his eyes as he sank to his knees, already reaching for her, gathering her in his arms as he knew all help had come too late. He softly shook her nonetheless, and as he cried harder at her lack of response, her boy began sobbing again as well, seeing the stranger's effort unsuccessful. Primal drive made him rock back and forth like a child as he cradled her against him, tears spilling down over his cheeks as he broke down entirely over her lifeless body.
The sound of a motorcycle – a flying one in particular – urged him to part from her, stilling his rocking motions as his heavy head fell against the bars of the wooden cot in which her son sat.
He stroked her hair one more time, knowing that he would have to tell her goodbye in a matter of seconds. Shifting on his knees to lower her to the floor again, Severus leaned in to let their foreheads touch, eyes falling shut for he couldn't bear to look into her unseeing ones. His lips brushed across hers as they parted, a trail of moisture left behind by his tears the only thing that could possibly betray his having been there… already evaporated by the time Sirius Black arrived to find his godson screaming but otherwise seemingly unharmed. By that time Severus Snape used one of the little magical techniques his Master, Lily's killer, had taught him to disappear into the night, six words of goodbye lingering after his departure, "I'll always love you, my Lily-flower."