The silence, after what transpired at the river banks was heartbreaking to her because she was the sole reason for him acting like this.
All he wanted was for her to tell him what she's been hiding,which was impossible,it's hard to open up after bottling everything inside for a long time.
Because she's starting to be happy,telling him that she was going to die in eight months time was already a mood spoiler, because he would start seeing her differently.
That's what she didn't want,she didn't want the pity that would be on his face once he finds out about her sickness,so it's for the best that she didn't tell him.
They were walking home,but with him in front while she was taking her steps slowly because she didn't want to see his face,walking back home with him was already hurting because she knew that things are not going to be the same again.
He knew.