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,
Unlearnèd in the world's false subtleties.
- Ah, now we get his motivation ("that" = "so that"). And what is it? Another deception. He wants to mislead her, to make her see him as what he is not.
- What's more, he wants her to see him as simple, naive, unsophisticated, "untutored" -- i.e., some one who has not had lessons in the world and its ways -- and as young.
- So at the same time as he is deceiving himself by believing her lies, he is lying (tacitly) to her by presenting himself (in effect) as "made of truth" -- "Unlearnèd in the world's false subtleties." Quite a complicated bit of game playing going on here!
- And his tone as he tells us this? Is he pleased with his little game? Or is there a touch of sadness as he mentions "the world's false subtleties" which he so clearly is not unacquainted with? (I suppose both elements can be heard.)