Disclaimer: everything belongs to J.K. Rowling and Warner Bros.
His mom thought Tom was a bad influence on him. She said that, since they started to walk together in school, Abraxas had become more aggressive, relapsed, stressed. He couldn't tell her it wasn't really Tom who changed him – it was Tom's goals.
When the Knights of Walpurghis were created, it wasn't much more than a group of study. They discussed everything: politics, magic theory, philosophy, astronomy. Anything that sparked an interest in someone would eventually become a subject of one of their meetings, simply because this was how the Knights were wired: they never overlooked curiosity, never ignored someone's desire for knowledge.
Although what some of their classmates assumed, Tom didn't take a special interest in dark magic. In fact, he favored discussions about History and Politics more than any others. That said, when they did talk about dark magic, Tom was the one who had more knowledge to share – somehow, he would always know about a long forgotten theory from this or that author; he would point them to a dust book which required blood sacrifice to be read; he would describe a ritual from an ancient civilization.
Abraxas had thought about asking Tom where – how – he found such information, but somehow the question always seemed to slip away when they were talking. Not because, unlike his mother's assumptions, he was afraid of voicing opinions to Tom. No, the reason Abraxas never brought those questions to light was simply because there was always something else more urgent to debate.
Did Grindelwald cast Imperius on Hitler? Could the Nazis succeed? How the addition of nightshade changed the effects on a love potion? Was there a connection between the elliptical rotation of planets and bird's migration?
Abraxas had always enjoyed intriguing conversations; he had been a very curious child, after all. But Tom, he sparked something different inside him: not only the desire to understand, but the want to uncover. And the Knights of Walpurghis debates served exactly to go a step further in knowledge.
Therefore, it was only expected that, eventually, they would go from the theory straight to the practice. Experiments became an everyday occurrence; their discussions became broader, deeper.
Their phrases shifted from "where did you read that?" to "did you prove that?".
Tom mediated most of those experiments, more often than not aiding them with a piece of information or a new way of facing a problem.
Abraxas hadn't realized, until then, Tom's ability to leadership - of course, their group had been his idea to start with, but their discussions had always been very democratic. Now, however, the brilliance of his classmate really started to shine through.
The more time Abraxas spent with Tom, the more he admired him. The more he desired to be his equal.
And the more aggressive, relapsed, and stressed he became.
Soon enough, Abraxas turned into one of the most devoted member of the group. He proved – or debunked – theory after theory; created new ways to cast spells; invented more efficient potions. Still, it wasn't quite enough.
Tom praised him, of course (he went so far as to say he "admired Abraxas") but there was something missing. Every moment Abraxas spent with something else other than his studies, he feared he was losing precious time.
He shouldn't be in the Quidditch match knowing full well he had yet to prove the connection between cold weather and the length of moonsugar.
How could he sleep when he was so close to reproduce Amortentia without the use of ashwinder eggs?
Should he dine or should he finish his paper about the aid of magic in the creation of the airplanes?
Inside Abraxas, there was always that something beating just next to his heart and pushing him forward, further than any of his classmates had gone thus far. Further than, maybe, even Tom himself.
That thought always made him smile. Tom could be more talented than him, but Abraxas could pride himself in working harder than him – harder than anyone else.
That belief, however, didn't last long.
He found out Tom worked just as hard as he did, only different, much darker projects. At the same time, Abraxas discovered two things about the other: his blood status, and the blood on his hands.
Tom, the half-blood, had killed people – four of them, thus far.
"For the sake of magic studies." He would justify.
The worse part? Abraxas believed him. He knew, deep down, he shouldn't. He knew he should be sickened by the very thought of Tom's deeds.
He wasn't. He was admired.
Tom's findings could forever shake the magic world were they to be revealed – his hypothesis, already wild; its proving, absolutely groundbreaking.
The two of them started to talk more, oftener, and about darker subjects. Now that Abraxas knew his secrets, Tom seemed to have lost something which completely changed his attitude towards him.
Much later, Abraxas understood that Tom lost his fear.
His mother's complaints worsened after this, but he started to worry less about what she thought or felt. He started to worry less about everyone, but Tom.
So what if he was stressed? Weaker? Paler? Aggressive?
Tom was also feeling all the terrible consequences to their tireless work, but he didn't have anyone to tell him to abandon his Works and Theories.
Maybe, Abraxas thought, that was the reason why Tom had always been slightly better at everything: simply because he didn't have someone to hold him back; simply because he didn't fear to pay the price.
And in a certain point, Tom did influence Abraxas:
They both agreed that raising a little hell in one's life was a small price to pay for Knowledge.