Even had you skill In speech – (which I have not) – to make your will Quite clear to such an one, and say, "Just this Or that in you disgusts me; here you miss, Or there exceed the mark" – and if she let Herself be lessoned so, nor plainly set Her wits to yours, forsooth, and made excuse, – E’en then would be some stooping; and I choose Never to stoop.
The Duke lists all the obstacles that prevented him from talking to the Duchess directly about his problems with her behavior.
He claims that he doesn’t have the "skill / In speech" (35-36) to explain what he wants from her – but his skillful rhetoric in the rest of the poem suggests otherwise.
He also suggests that she might have resisted being "lessoned" (40), that is, taught a lesson by him, if she had "made excuse" (41) for her behavior instead.
But even if he were a skilled speaker, and even if she didn’t argue, he says he still wouldn’t talk to her about it.
Why? Because he thinks that bringing it up at all would be "stooping" to her level, and he refuses to do that.
Oh sir, she smiled, no doubt, Whene’er I passed her; but who passed without Much the same smile?
The Duke admits to his listener (who is this guy, anyway?) that the Duchess was sweet to him – she did smile at him whenever he passed by her.
But, he says, it’s not like that was special. She smiles at everyone in the same way.
This grew; I gave commands; Then all smiles stopped together.
The Duke claims that "This grew" (45) – that is, the Duchess's indiscriminate kindness and appreciation of everything got more extreme.
The Duke then "gave commands" (45) and as a result "All smiles stopped together" (46).
Our best guess is that he had her killed, but the poem is ambiguous on this point.
It’s possible that he had her shut up in a dungeon or a nunnery, and that she’s as good as dead.
She’s not his Duchess anymore – she’s his "last Duchess" – so she’s clearly not on the scene anymore.
There she stands As if alive. Will’t please you rise?
The Duke ends his story of the Duchess and her painting by gesturing toward the full-body portrait again, in which she stands "As if alive" (47).