I think the blame is of course on the writers, they suddenly decided to put them aside, change their characters, make it seem they forgot about each other
they were bipolar with Jeremy, but I think they didn't do justice with Bonnie neither, she basically forgot about Jer too in season6, which made no sense
As usual they didn't know how to handle them, which is a shame, bc the end of season5 had so much potential for them, the fact they were separated, the struggle, it could have end differently and it would have been better
