Remus might have argued further about Peter. He knew Peter had wanted to talk to Sirius and James, James in particular first. But, if James hadn't managed it, Remus wouldn't push it. He would just do his best to remain friends with Peter as he could.
More than that, however, he couldn't very well argue about Peter when he had to literally bite his tongue to prevent himself from laughing darkly. Huge roles, they said. Just like with Harry. Gods, they were still stuck in nineteen eighty and he really didn't want to go back that time, back to the way things had really been when Harry was a baby and the two people sitting in front of him thought Remus was working to hand them over to Voldemort. They hadn't trusted him enough to be a huge part of Harry's life then. By those words, they were practically telling him he wouldn't be again.
They likely didn't mean it that way, but that was how it sounded and Remus couldn't help feeling the old hurts.
It just got worse when Lily started to chastise him for his words about Harry, as if he'd implied anything other than sorrow his friend wouldn't know his little brother or sister.
"That was not what I said, Lily," he said finally. "I never said anything to imply you didn't care about Harry. But, you are right when you say I don't know you. I know a memory of you that's eight years old, the same as you know a twenty-one year old version of me that hasn't existed since the day you died. Life has taken us all in different paths, not only since we came back, but really, since we were eighteen. And all the excuses in the world about second chances are worthless unless we can all be honest with each other and admit that fact. Things have changed and while I think we all still consider each other friends, it's not the same.
"It's as simple as that. Whatever the excuses we tell ourselves, the real, honest truth is that there used to be a day when it didn't matter what the situation was, the other three would be the first we even thought of sharing anything with when something happened. But, we're not those people any more and until we can all accept that our lives are changing, we're going to keep doing this to each other because our expectations no longer match reality."
Unreasonable expectations were going to destroy the friendship they had left and, despite the fact that at that moment he thought this entire conversation was inconsiderate and thoughtless, Remus didn't want to see this be the way their friendship ended.