How does Walton feel about Victor's death?

In Mary Shelly's Frankenstein, Robert Walton is an explorer on an expedition in the Arctic. His ship has become trapped in the ice. He sees a man floating on a sheet of ice and brings him into his ship. This man is Victor Frankenstein. He tells Walton his life story and Walton records his tale.
As Walton listens to Frankenstein's story, he becomes incredibly attached to him. He is astonished by Victor's life and admires him. Victor's description of the monster fills him with horror. Since his appearance on the boat, Walton has been able to think of nothing else.
At this point, Victor is very sick and depressed. He longs to die, which grieves Walton. He writes to his sister, saying:

Must I then lose this admirable being? I have longed for a friend; I have sought one who would sympathize with and love me. Behold, on these desert seas I have found such a one; but I fear, I have gained him only to know his value, and lose him.

Walton is heartbroken by Victor's death. Once again, he writes to his sister and says:

What can I say, that will enable you to understand the depth of my sorrow? All that I should express would be inadequate and feeble. My tears flow; my mind is overshadowed by a cloud of disappointment. 

Walton has gained a friend only to lose him. He knew Victor for a week and treasured his friendship in the short time they had together. Once the ice breaks up he sails back to England, where he hopes to find consolation for his pain.