When my love sweares that she is made of truth,
I do beleeve her though I know she lyes,
That she might thinke me some untuterd youth,
Unlearnèd in the world's false subtilties.
Thus vainely thinking that she thinkes me young,
Although she knowes my dayes are past the best,
Simply I credit her false speaking tongue,
On both sides thus is simple truth supprest:
But wherefore sayes she not she is unjust?
And wherefore say not I that I am old?
O loves best habit is in seeming trust,
And age in love, loves not t'have yeares told.
Therefore I lye, with her, and she with me,
And in our faults by lyes we flattered be.
In the first quatrain, the poet states that, though he knows his mistress is lying, he nevertheless believes her, and this because he wants her to think he is an untutor'd youth and unused the the lying subtleties of the world, therefore younger than he is.
In the second quatrain, the poet explains that there are thus lies on both sides
In the third quatrain the poet asks why it is necessary to tell these lies. He finds the answer in the fact that firstly, in love, it is best to trust, and, secondly, it is better not to be reminded of one's age.
The final couplet expresses resignation to the situation: the poet and his lover lie together, ie sleep (lie) together and deceive (lie to) each other. Thus harmony reigns.