What does Victor consider when he says,"I was tempted to plunge into the silent lake, that the waters might close over me and my calamities...

In Volume II, Chapter I, Victor has been mourning both the loss of his brother, William, as well as the execution of his family's friend, Justine, who was convicted of murdering William.  He says that he was often "tempted to plunge into the silent lake, that the waters might close over [him] and [his] calamities for ever."  His guilt and sorrow have thus prompted him to consider taking his own life by drowning himself in...

In Volume II, Chapter I, Victor has been mourning both the loss of his brother, William, as well as the execution of his family's friend, Justine, who was convicted of murdering William.  He says that he was often "tempted to plunge into the silent lake, that the waters might close over [him] and [his] calamities for ever."  His guilt and sorrow have thus prompted him to consider taking his own life by drowning himself in the lake.  

It is only when he considers "the heroic and suffering Elizabeth" that he resolves to continue living because he does love her and because they are meant to marry.  Further, he thought of his "father, and his surviving brother" who he would also leave behind if he died now, and "There was always scope for fear, so long as any thing I loved remained behind."  Victor knows that his loved ones are in danger because of his murderous, on-the-loose creature, and this helps to convince him to remain alive so that he can try to protect them.