A Samifer fic? In my 2023? It's more likely than you think. Obviously, I don't own the rights to Supernatural. Enjoy!
Lucifer hated Sam; he hated how he could not have him. Out of all of humanity, even the one who had been created for him alone had chosen to reject him. He could have given him anything he'd ever dreamed of. Lucifer could- and would- have made Sam a prince, a king, a god of a new world. He would have done anything for him, anything Sam had asked for. Apart from the one thing Sam truly wanted. Time and time again, Lucifer would offer to give him the universe and all that lay beyond it. And Sam's answer would always be the same.
"I want you; just you. No plots, no power, no manipulation, no revenge. Just you and me, together. Side by side for as long as Fate will allow,"
But no matter how hard he tried, that was something Lucifer simply could not do. He needed power; he would be utterly lost without it. Power allowed him to protect himself, to protect Sam. It meant he could keep them as far away as possible from the harm of his father's hand. But, for reasons seemingly beyond Lucifer's understanding, Sam couldn't see that. All he saw was Lucifer choosing power over him, time and time again. And he just couldn't take it anymore. So, he had told Lucifer that he had to go. If the archangel couldn't leave his power, Sam knew he had to leave him instead. Lucifer had refused, of course. But it seemed that Sam wasn't taking 'no' for an answer. He pushed Lucifer away at every opportunity. It broke his heart, his very soul, but he couldn't bear to be second best to Lucifer's lust for power anymore. He would always care for him, that was something he could never escape. But Lucifer wouldn't, or couldn't, do the same. Not in the way Sam needed him to. So, Sam continued to push him back in the hopes that eventually Lucifer would simply give up and walk away. But what Sam hadn't been expecting was that the Prince of Darkness did not seem to be above begging. And that's when the tears and pleading had started. At first, Sam had thought it was just another trick, a way of manipulating him until Lucifer finally got what he wanted. But the longer it continued, the more Sam started to believe him. Suddenly all that pride and vanity fell away, leaving nothing but Lucifer's pain and longing in its place, plain for Sam to see and so connected to his own feelings. In an instant, Sam could feel himself slipping back into Lucifer's grasp. But, unlike before, when Lucifer would reach out and roughly take back 'what was his', he instead did nothing. He simply allowed Sam to come to him, his feelings still bare and a perfect reflection of his own emotions, like looking into a mirror. Never before had he felt everything Lucifer felt so acutely- the loneliness, the sadness, the longing, the fear. All of these were emotions and feelings that Sam had known from Lucifer before, one way or another. But the one thing he truly hadn't expected to feel was love. It was coarse and painful, bold and desperate, all-encompassing and judgement clouding. But it was there. And it posed an utterly undeniable truth.
Lucifer loved Sam.
He loved him with every atom of his cosmic being. He loved him in a way so powerful that it was almost impossible for a mortal mind to comprehend. He loved him the way the stars loved the moon and the way spring loved summer. Lucifer loved Sam the way God had loved his most precious creations...
Sam all but collapsed at the realisation, his heart crushed under the weight of all that raw and beautiful celestial emotion. But Lucifer was there to catch him as he fell, just like he always was. In that moment, Sam had begun to understand; made for each other, two halves of the same whole, soulmates, it all became so clear to him. And that is how Sam Winchester truly fell in love with the devil, because he realised the devil would always love him back, no matter the cost.