If this be error and upon me proved,

Question

I never writ, nor no man ever loved.

These lines are an example of a/an

Answer 1

Imperfect rhyme?
http://en.wikipedia.org/wiki/Rhyme#Types_of_rhyme

Couplet?
http://en.wikipedia.org/wiki/Couplet

A sonnet's concluding couplet?
http://www.shakespeare-online.com/sonnets/116.html

Could be several things!!