If Elena was staying with D and F most of the plot would be negated. How could D and F spend any quality time alone with Elena there, since the three of them are sexually active together now? How could the D+Martin thing happen with Elena around? Elena is slutty and unless D told her she wanted to have sex with Martin Elena would be chasing him, but then D would have to admit to Elena she is looking for more male sex partners than F. How would Elena react to the news that D is getting sexually bolder, and not just with women. The D+F+Georgina sex would have been awkward if Elena was living there, if not impossible.
So Elena not living with D and F seems to be a result of having to move the plot forward.
IMO ironically on the D only path Elena living with D and F would seem to have less plot impact.
It is likely that Elena will at some point move in with D and F, depending on your pah.