Chapter IV, of Mary Shelley's Frankenstein, defines Victor's feelings regarding Justine's death. Overwhelmingly, Victor feels responsible. At the same time, Victor is angered and saddened by the fact that he is still alive (and Justine is dead). As with other deaths in the novel, Victor falls tumultuously into a depressive state.
Sick with regret and remorse, Victor only found happiness in nature. The one thing which allowed him to find peace was his boat rides out onto the lake.
I was often tempted, when all was at peace around me, and I the only unquiet thing that wandered restless in a scene so beautiful and heavenly.
Although Victor found nature relaxing and peaceful, he could not find peace for himself. Essentially, Victor used nature to find the peace he so desperately needed to contrast the "house of mourning" he and his family were living in.