In "The Yellow Wallpaper," what is the significance of this line to the changing relationship of the narrator and her husband?"Lay there for hours...

The line you ask about from "The Yellow Wallpaper"
demonstrates that the cure prescribed for the narrator by her husband (and the
male-dominated medical establishment as a whole) is failing miserably.  It demonstrates
that denying a depressed woman all intellectual and mental stimulation to cure her is
ludicrous. 

In Gilman's day the male medical establishment
believed women were mentally inferior to men and that too much thinking made women
ill.  Doctors also believed that female mental illness was rooted in the ovaries (thus
the term hysteria, another form of the word,
hysterectomy). 

The quote reveals a woman suffering from
what we today would call post-partum depression finding mental stimulation any way she
can.  Forced to give in to her husband's every order, her growing insanity is a
testament to the destruction of whatever relationship they once had.  As she "sees" the
wall paper come alive, the "distance"
between her and her husband
grows. 

The line you ask about doesn't directly deal with
her relationship with her husband, but it indirectly exemplifies their decaying
relationship.