Antonio is a melancholy man who bestows his wealth on his friends, particularly Bassanio. He says he has no idea why he feels sad and rejects Salarino’s suggestions, denying that his merchandise makes him sad. The conclusion is that Antonio simply has a gloomy nature.

Though Antonio replies, “Fie, fie!” when they say he is in love, many posit that Antonio actually loves Bassanio. He sacrifices so much for the young man. Bassanio, a spendthrift, admits that he owes Antonio “the most, in money and in love,” but Antonio still offers him more: “My purse, my person, my extremest means, / Lie all unlock'd to your occasions.” Without thinking twice, Antonio makes a dangerous bargain with his enemy Shylock, breaking his moral code and promising to pay a pound of his own flesh if he does not repay the borrowed money on time.

When Antonio does not repay Shylock on time, Shylock insists on their bond. Antonio accepts his fate with resignation, only praying that “Bassanio come / To see me pay his debt, and then I care not!” He never regrets making the deal. Antonio tells Bassanio to tell his wife of his love for him: “bid her be judge / Whether Bassanio had not once a love.”

Also telling of Antonio’s affection for Bassanio is this report of their parting:

SALARINO: And even there, his eye being big with tears,
Turning his face, he put his hand behind him,
And with affection wondrous sensible,
He wrung Bassanio's hand; and so they parted.

SALANIO: I think he only loves the world for him.

Perhaps Antonio suffers from depression, perhaps Bassanio is the son he never had, or perhaps Antonio is in love with Bassanio. Whatever the case, there are many motives of which Antonio himself might not be aware.