Lucius and Severus, again
Severus couldn't really tell you how or when his and Lucius's relationship became so...intimate.
Lucius was a rich pureblood, a child of blood supremacists. Severus was a half-blood who grew up in a poor non-magical town....So, obviously, they didn't know each other until Hogwarts.
They met briefly on the train ride to start their first year. Lucius was looking for Narcissa, they had been friends before she came out, but Lucius's parents forbid him from interacting with her after she told everyone she was a girl, because of that he was desperate to see her. Severus didn't know who Narcissa was, but offered his help anyways. They found her, and that was the end of that. It could have been the end of their partnership, except for what happened at their sorting.
Severus had always been anxious, but his first year at Hogwarts was the worst. The sorting incident started with his anxiety, after Lily was sorted into Gryffindor. He thought it meant she wouldn't want to be his friend anymore, they both already knew he would end up a Slytherin, which was terrifying.
It was a long time before Severus's name was called, after all there's a pretty big gap between 'E' and 'S', and Severus spent the whole of it panicking. He would have been anyways, but the Lily situation made things more unbearable....Then his name was called.
He didn't move, barely heard it. People started yelling at him to go, one person pushed him. It was gentle, but he was unstable enough already to just fall to his knees. That was all embarrassing enough, but it didn't end there.
Crying.
Severus fell to his knees and began sobbing. Everyone was staring, some laughing, making remarks. Not only was he never going to live this down, but it would be a lot worse in the moment because he had no way to calm down.
Enter Lucius.
Lucius was already sorted, of course, his last name started with an 'M' after all, but that didn't stop him from going back to the group of S-Z students. It didn't stop him from claiming that Severus was his best friend, enough to shut most of the purebloods up. It didn't stop him from helping Severus stand, walk to the stool, then leave the Great Hall after the hat called 'Slytherin'.
They walked out into the Entrance Hall, where you first entered the school. All that was there was a bathroom, storage closet, the door to the Great Hall, and a staircase. Lucius brought him to the bathroom to clean up, and calm down.
It still wasn't over. He was humiliated, friendless(or so he thought), and would never be able to face his classmates again. For some reason, he admitted that all to Lucius, who smiled. That reaction confused Severus quite a bit.
Lucius informed him that humiliation was not a big deal, he could face them again. That even though Severus thought it was horrible, most people would push it out of their minds by tomorrow(especially the other first years who were mostly just anxious about starting school). And that although he was unsure about Severus's other friend situations, he was his friend.
Usually Severus didn't think you could become friends so quickly with someone, but....This was different....They were friends, he could feel it.
Somehow they managed to stay friends through it all. Severus wasn't sure that he would have stayed friends with himself based on how he was in third year, but Lucius never left. Never gave up on helping Severus.
Severus didn't really think he deserved it, but....He was still incredibly grateful. He didn't know what he would do without Lucius.
They were meant to be.