What does the line 'I never writ, nor no man ever loved' imply?

Shakespeare, in his poem Let Me not to the Marriage of True minds, approaches the idea of love or ideal love, the other way round. Throughout the poem, he talks and explains all the negatives that an ideal love must not comprise. Similarly, the poet maintains his tone in the end of the poem as well. He closes the poem with the couplet 'I never writ, nor no man ever loved'. In an unnatural or inverse fashion, rather than saying that men have loved and so he writes, Shakespeare says that if what he has written is to be an error, then he would not have written it all and that no man would have loved at all. Confidently, he challenges anyone to prove his idea of love to be wrong; he knows that it is impossible and that his knowledge stands true.