Moraders (Harry Potter)

Teachers and Snape during his studies
Dumbledore. Even during his school years, Dumbledore noticed Snape and recognized his abilities, but he also noticed his surroundings. Later, it was this attentiveness that allowed Dumbledore to understand Snape's soft spot for Lily—and to later build on it.
McGonagall. As the head of Gryffindor House and a strict teacher, she hardly singled Snape out. Her attitude was rather formal: she valued academic success, but didn't turn a blind eye to questionable connections and behavior.
Slughorn. The Potions Master greatly valued Snape's talent. He was one of the top Potions students, and Slughorn encouraged this: he praised him, promoted him, and gave him additional opportunities. It was in Slughorn's class that Snape truly blossomed into an outstanding Potions Master, though he remained reserved and abrupt.

Madam Pomfrey is a nurse at Hogwarts and the head of the hospital wing. During Snape and the Marauders' time, she treated students for a wide variety of injuries and ailments using potions and magic.

What did she usually do?
She treated injuries after skirmishes. Considering the number of conflicts between houses, and specifically between the Marauders and Snape, Madam Pomfrey must have treated the injured more than once: reducing swelling, healing cuts, and resetting dislocations.
She helped with magical complications. If a spell went wrong or someone overdid it with a potion, she knew how to counteract the effect.
She monitored the secret situation with Remus. She knew Remus Lupin was a werewolf and assisted him: she accompanied him to the Whomping Willow before his transformations, ensured everything was as safe as possible, and dealt with the consequences when necessary.

The Marauders and Snape
The Marauders (James Potter, Sirius Black, Peter Pettigrew, Remus Lupin) and Snape were classmates: the Marauders were a couple of years ahead of them. Their relationship was hostile from the start due to house differences (the Marauders were Gryffindor, Snape was Slytherin) and personality clashes.

Bullying. James and Sirius openly bullied Snape: they made fun of him, used spells, and humiliated him in public. The most famous episode was when James suspended Snape in the air and left him dangling upside down.
The Role of Remus and Peter. Remus didn't participate in the bullying, but he didn't stop his friends either—he felt awkward, but he didn't go against the group. Peter mostly supported the others.
An extreme prank. Sirius lured Snape to the Shrieking Shack when Remus, now a werewolf, was supposed to be there. It was a truly dangerous prank: Snape could have died. At the last moment, James stopped him and essentially saved him, but Snape wasn't happy about it: he didn't trust James's good intentions and hated him even more.
The backlash. Snape wasn't sitting idle: he was trying to catch the Marauders, gathering dirt on them, taunting and picking on them, so the hostility was mutual.
Snape and Lily
Snape and Lily had been friends since childhood and continued to communicate at Hogwarts, but their paths gradually diverged.

The Beginning. Snape was the first to tell Lily about magic and Hogwarts; she was the closest person to him. They supported each other at school, but they ended up in different houses and social circles.
The Schism. Lily grew increasingly uneasy about Snape's company: among his Slytherin acquaintances were those who dabbled in the Dark Arts and despised Muggleborns. She begged him to stay away from them, but Snape wouldn't listen.
The Breakup. A turning point occurred in their fifth year: during an argument, Snape angrily shouted the insult "Mudblood" at Lily. For Lily, this marked the end of their friendship: she couldn't forgive him. Snape later tried to apologize, but she didn't accept it.
Marauders (They call me names) They call me nyudius, it's offensive