In the book hachet why does brian feel the fire is his friend?

Brian feels this way because he is stranded, all alone, and his mind is trying to get something as close to a person as it can .

EDIT:

I believe it is because it is one of the few things that he has seen in nature that is actually helping him survive in this difficult situation. (ie. It's keeping him warm, cooking the food he is able to find, etc.)

Hope this helps :D