Minerva McGonagall is a strong woman, thank you very much. She has fought in battles with the best of them and survived more duels than she cares to admit. She would much rather speak of her students- the ones with natural talents, the ones that lacked that talent but rose to the top through sheer determination. She also, though she hates to admit it, has had favorites. Four in fact.
Four boys who she watched turn her castle upside down and earn more detentions than previously thought possible. Four friends who she watched grow from bumbling preteens with either too much confidence or not enough. She watched them astound the world with their prowess and secretly marveled that she had been part of their education. And though she probably yelled at them more times than any other student she has ever had, she admits she adored them. There was something about their youthful exuberance, their attempts to lighten up their fellow students, their love of a challenge and incredible amount of courage and determination that won her heart.
It was the type of friendship that seemed as if it would never end. The bonds just grew tighter with every argument and triumph. It was the type of friendship people envied. The type everyone wanted but couldn't find. Minerva McGonagall is a very sensible woman, and she does not believe in Fate. But even she admits that there was something uncanny about how perfectly those four fit together. Maybe that's why it hurt so much to see it shatter.
She collapsed when she heard the news. Lily and James dead? She was sad about Lily- no question about that, but she had to admit her first thought was for Sirius, Remus and Peter. What would happen to them? How would they deal with it? Sirius would be devastated. James was his brother in all but blood- closer than anyone she had ever met. She couldn't even picture them without one another. She knew Sirius would never be the same- this was a tragedy Sirius might not survive this. Remus would be in shock. She always felt that it was James who had reached out and pulled Remus into their group. He was such a shy boy with such a horrible secret… But he would pull through if only for Sirius and Peter. They were his only family. But Peter, Peter worshipped James and Sirius he would be lost. Peter was always a follower. He might breakdown. She didn't know.
But when Albus told her that Sirius had betrayed them and then killed Peter? She couldn't fathom it. In fact, she told him that was an inappropriate joke at this time and that he should be ashamed. She didn't leave her rooms for a week when she found out it was true. It still embarrasses her that she didn't go visit Remus. She should have, but somehow she preferred to pretend that all of the Marauders had simply winked out at the same time. After all, it was much easier than admitting the truth.
She'll never admit how much it hurt to see Harry Potter on his first day at Hogwarts. She'll never admit how hard it was to have Remus Lupin teaching with her. She couldn't help but almost ask him where his cohorts were or refrain from crying when she saw how changed he was. His emptiness broke her heart. She'll never admit how horrified she was to find out Sirius was innocent. It would make it real.
Professor McGonagall is a very truthful person, thank you very much, but she still lies to herself about the marauders.