Let me not to the marriage of true minds
Admit impediments. Love is not love
Which alters when it alteration finds,
Or bends with the remover to remove:
O no! it is an ever-fixèd mark
That looks on tempests and is never shaken;
It is the star to every wandering bark,
Whose worth's unknown, although his height be taken.
Love's not Time's fool, though rosy lips and cheeks
Within his bending sickle's compass come:
Love alters not with his brief hours and weeks,
But bears it out even to the edge of doom.
If this be error and upon me proved,
I never writ, nor no man ever loved.
Shakespeare is saying that his definition of love may be thought by some to be erroneous. Note that life’s realities are disregarded in this sonnet — hardship, poverty, illness, physical and mental abuse, flawed human nature can undermine and destroy love. No doubt he could be accused of exaggeration and ignoring the realities. 
 But this poem, as frequently in the sonnet genre, is about ideals. Furthermore, it is known that poems were circulated amongst educated circles, and they did not necessarily reflect the poet’s true emotions, but were intellectual exercises. However, many academics believe that this sonnet (and all the others in the sequence) were reflections of Shakespeare’s true feelings; the intensity and beauty certainly suggest they were. If this is the case, we can say that the last couplet is a sincere and lovely conclusion. 
 Therefore, Shakespeare is posing a question in the last couplet. ‘I may be in error and it may be proven to be so. But if that’s the case then there is no point in writing or loving.’
Sonnet 116