In this poem, the speaker is addressing not the reader but the artist's wife, and we read his art of their conversation and thus deduce hers. Browning's style, in his dramatic poetry, requires the reader to work and infer what is meant from what is said—which may be its opposite.
In these selections from the poem 'Andrea del Sarto', we see the artist as, in essence, a weak man who has sacrificed his artistic integrity in obedience to his wife's immediate demands. We can see that del Sarto is besotted with his Lucrezia: he is eager to receive such signs of tenderness as the touch of her hand when next he gives her money; and he plainly adores her physical form:
"—How could you ever prick those perfect ears,
Even to put the pearl there!"
He gives, apparently as an excuse or justification for 'wasting' time looking at her, the fact that she must be the model for his pictures—presumably to remove the need to pay a model.
The painter is plainly aware that he disappoints his wife, and that what he offers her is inadequate, and he has to keep buying moments of her affection. In the eighth line of the poem "And shut the money into this small hand", it is made perfectly clear that his wife's favours are available only when he pays for them, and subsequently it appears that he is not the only man who can purchase them. He attempts to outbid the 'Cousin' but ruefully acknowledges that the Cousin pleases her more, somehow, and makes no serious attempt to oppose her will.
The picture that emerges of Lucrezia, the painter's wife, is of a cold, mercenary and manipulative beauty who has no love whatever for her husband. She does not notice—or care about?—his exhaustion, and it is clear that she expects him to be constantly at work, from the way he excuses his moments of rest by telling her he will work better when he is refreshed. Lucrezia obviously considers her husband's artistic ability merely as a commodity, and has no interest in any artistic integrity or real excellence: at the beginning of the poem she has obviously got a commission for Andrea which he does not really want, and at a price set by the customer, who also intends to dictate how and when the painting is to be done. Later, the painter muses on what he could do if he were back in France, free to paint as his inspiration dictates. But at once he is back again in the sordid reality of his commercial dealings, in order to pay for what his wife would bestow elsewhere. Indeed, Andrea admits that his own abilities should put him on a par with other painters of acknowledged greatness, but they had no wives:
"so—still they overcome
Because there's still Lucrezia..."
He understands that she trammels him, yet at the same time refuses to admit the truth, because he loves her.
It is clear from the narrator's attitudes that he is making the best of the situation and pretending to himself that he has chosen his present life. He characterises his work and his life as "A twilight piece", having toned down "My youth, my hope, my art" in accordance with the acquisitive demands of his wife. He has, in fact, some recognition of his own talent; he knows that if he could but paint as he wants to, he would be judged great. But he tells himself that he has few regrets. The poet is able to convey very clearly the painter's self-deception, and indeed his complicity in his own misery. For Andrea treats Lucrezia on terms she has dictated, and has abandoned his own wants and needs to defer to hers.
According to Giorgio Vasari, Andrea del Sarto was a very talented and inspired artist, but lacking in the 'boldness and daring of spirit' to make him truly great (and put him on a par with the Leonard, Rafael and Agnolo to whom he compares himself). In this poem, it is clear that the painter's own weakness, combined with the heartless venality of his wife, combine to reduce his potential genius to the status of a painter who paints to order.
The 'marital tragedy' view of this poem is certainly valid. The reader can pity del Sarto for his helpless adoration of an unworthy and unfaithful wife. It is obvious that he is unhappy in his marriage, and fooling himself into believing he is content. However, it is not only a tragedy of a marital nature. In this case, there is also the tragedy of talent unfulfilled: del Sarto might have been truly great, but failed to achieve real greatness through the defects of his own character and his wife's. The marital tragedy might have been written about a clerk: in this poem, marital misery is entangled with the loss of artistic integrity.