When my love swears that she is made of truth,
I do believe her, though I know she lies,
That she might think me some untutored youth,
Unlearn`ed in the world's false subtleties.
Thus vainly thinking that she thinks me young,
Although she knows my days are past the best,
Simply I credit her false-speaking tongue:
On both sides thus is simple truth suppressed.
But wherefore says she not she is unjust?
And wherefore say not I that I am old?
Oh, love's best habit is in seeming trust,
And age in love loves not to have years told.
- "Habit" here is a clothing metaphor (cp. "monk's habit"). The best covering that love can possibly wear, he's saying, (and the best routine behavior to sustain love between lovers) is an appearance of trustfulness. Pretty cynical and bitter, no?
- "Told" in the next line draws on its more literal meaning too -- to "tell" is to count (cp. "bank teller"). So the old lover doesn't like to have the years counted, even, much less blabbed about to others or even between the two lovers.
- What's the effect of that "Oh"? I hear it as a weary sigh, not unmixed with a sad humor.