His promise

Sirius Black promised to never leave Nellie Jerome. He did though. He broke the promise when they were kids, when he was sent to Azkaban, and when he died. Nobody understood why it was such a big deal when he broke it the first time and the second time. But the third time something was different. She didn't yell, she didn't scream, she fell, She broke. They all asked her what was wrong and she simply said. "He didn't know I was never truly mad." they had no idea what that was supposed to mean. She was as mad as a hatter but she didn't mean it that way. So to clear things up a bit, the summer after he died she was going to explain exactly what was between them. Nobody knew except James, Lily, Remus, Peter, Her, Sirius, and a few others but the ones alive were never to speak of it. It was her wish. To never have that part of the past ever spill out of the lips of anyone. That's probably why Remus Never questioned why she didn't scream or yell. It was already replaying in her mind again.