Thanks, everyone! These are brilliant ideas which all make perfect sense when you point them out, especially the bits about Remus not finding work after Hogwarts and things getting him down. I could see him distancing himself from others because of that.
And Carole, I don't know if you saw my response elsewhere but it's like you are reading my mind when it comes to Peter! I really wondered if he was capable of putting the bug in their ears, so to speak, and able to play them off each other. He demonstrates exceptional cunning running the double-cross for so long, after all, and manages to frame Sirius and go into hiding for twelve years - so he wasn't as dumb or weak as everyone though. I'm glad the possibility doesn't scream OOC on Peter's part!
As for Lily, I want her to be the one who trusts Remus implicitly. But James might be ultra-protective of his son for sure.
You mentioned Remus having a spectacular temper - I'm curious where? I can totally see it but can't recall the evidence of it other than the fight with Harry in DH.