I think you have to be very careful not to portray Peter as this person who always thinks he's worthless. I think he was insecure, but whilst at Hogwarts he was in with the 'cool' gang. He had a worth to them and felt validated somewhat by their friendship. I think there'd be moments when he does feel irritated and slighted but not many. Remus, for one thing, isn't perceived to have been as cruel as Sirius, for instance.Originally Posted by Royari
But ... Peter probably didn't think Remus was worth as much as Sirius because Remus was never going to be wholly accepted by the magical community.
To be honest my feeling with the Marauders is that there dynamic changes as soon as James and Lily become a serious item and it's not just James chasing after a girl. James has a new priority outside the group. Sirius is always going to be okay because he's secure enough in their friendship (although a bit of jealousy could be interesting), Remus has always been that bit more detached from the group because he knows he's different. Peter is the one with the problems as the group fractures.
Also, when do you think the Death Eaters first started courting him, and how long do you think it took him to give in?
I have a few theories about this. One is that on leaving Hogwarts he came into contact with DE's working at the Ministry (See The Slow Burn of Betrayal and the first chapter of Apparently Asleep which hints at this). Then there's his feelings during the seventh year when the Marauders were thinking beyond Hogwarts and possibly breaking up. In the big bad world, Peter would be without his friends. (Wormtail on the Hogwarts Express)
But you could also look at the DEs (or wannabee DEs) who were still at Hogwarts. JKR has hinted that Voldemort tried to recruit James and Lily while they were at Hogwarts (the first example of them defying him), it could be that Peter was recognised as a weak link by the DEs at that point. They always seem to have a good head for strategy.