Chris buried the bent duck in the barbussy because it was right in his house and didn't require effort. At the time he arguably had a non-related girl his age interested in him, but that was going to require work. The level to which Barb did or did not resist is debatable, but she was unable or unwilling to take action between the "scheduled" sessions. Barb was a shut in, and Chris basically was too. This is why I had concerns about Chris in a group home. He would have access to people who wouldn't resist in a significant way and would not require him to leave the building. Basically a situation similar to Barb.
Chris has an MO of laziness and access.
We don't know a bunch about Flutter, but unlike Barb she not only comes and goes, but appears to do so by airline travel. She also seems to be in control to some extent. She was reported to have talked Chris down when they got booted from the animate convention. She was heard shushing him at the Italian restaurant. Flutter is not similar to Barb from a victimology standpoint. I'm not worried about her falling victim to the bent duck.