I'm a total Peter/Eva shipper, but I agree that the whole 'okay suddenly they're in love again!' thing was really written out. I mean, Eva had been a slave for seven years, tortured, presumed dead, and probably deprived of human contact for extended periods of time. She's going to be DAMAGED. Woman's going to have serious issues. It's not like as soon as Edriss is dead she'll just be fine and happy and go right back into the mommywife role.
My personal theory/headcanon is that Peter always had some emotional issues even before Eva's 'death' and kind of deferred responsibility to Eva, was getting therapy after #5, was able to kind of grow up and get more stable leading up to and during his marriage to Nora, and then, when reunited with Eva (who was in pretty desperate need of patience, love and TLC post-Edriss), was forced by circumstance to stay the responsible, adult one and use what he learned in therapy to help Eva.
As for Nora, I've written fic about her, and I know at least one other person has too, trying to figure out what happened to her. It's one of the most frustrating loose ends in the series. I can't see Marco telling Peter or Eva 'lawl I lied she was free all along' unless he knew that Nora was alive and well, but if she was...I don't know how that would play out.