In chapter 22 of Mary Shelley's Frankenstein, Victor receives a letter from Elizabeth which details her concern for both him and the "favorite plan" (Victor and Elizabeth's marriage) of Victor's parents. In the letter, Elizabeth openly voices her concerns about Victor's health and well-being.
"Yet I fear that the same feelings now exist that made you so miserable a year ago, even perhaps augmented by time. I would not disturb you at this period, when so many misfortunes weigh upon you."
In these lines, Elizabeth is voicing the fact that she fears Victor may be miserable again (the first time being when he returned home from Ingolstadt after creating the creature and finding out the William had died by the creature's hand). While Elizabeth does not know about the creature, she believes that Victor's sorrow and miserable demeanor lies in the fact that he cannot get over the deaths of both William and Justine (the Frankenstein servant charged with the death of William). Unbeknownst to her, Victor's "illness" lies in the fact that he has created a life which has destroyed the lives of those who meant the most to him. He, as he numerously states, is ultimately responsible for the deaths of both William and Justine. He is the one who brought the creature to life and abandoned him.
Therefore, the quote simply refers to the fact that Elizabeth believes that Victor is still suffering from the untimely deaths of William, Justine, and Henry Clerval (the creature's latest victim). She realizes Victor has faced much loss in his life and does not feel it necessary to bring more pain upon him.
Following the paragraph the previous quote is taken from, Elizabeth is reminding Victor of the marriage hopes Victor's parents possessed. As stated, Elizabeth knows that Victor has been through much, and she does not wish to further burden his load by asking about their hoped union.