Freeze, freeze, thou bitter sky,
that dost not bite so nigh
as benefits forgot;
the comparison in the passage above can best be rewritten as

the cold of the air is not as harsh as forgotten favors
the sky is frozen, but that is no worse than my loss of power
although the air is cold, friendship will keep us truly warm
the inhumanity of people is almost as bad as winter

Isn't it personification? Because the personification here is "That does not bite so nigh". By saying it bites, you are personificating it. ( If that makes sense

The comparison in the passage above can best be rewritten as "The cold of the air is not as harsh as forgotten favors"

Explanation:

These lines make the comparison of the lack of gratitude of people and how does this reacting make other who are affected suffer, it is not talking about actual freezing or cold, it is about the insensibility of some and even more the coldness of humanity towards the ones that were of help for them in the past and from whom they got some benefit.

im not sure about this one