How we cite our quotes: (Act.Scene.Line). Line numbers correspond to the Norton Shakespeare edition.
Quote #1
ANTONIO
Well, tell me now what lady is the same
To whom you swore a secret pilgrimage,
That you today promised to tell me of? (1.1.126-128)
Bassanio's love life is the first thing Antonio brings up with Bassanio when they're alone together in the play. Maybe he's just one of those guys who likes to gossip, or maybe Bassanio has been on his mind. Bassanio's new courtship seems likely to be the source of Antonio's sadness, as it's at the forefront of his mind. Antonio clearly cares deeply about Bassanio as a friend, and he's facing the fact that he might lose him to this woman.
Quote #2
BASSANIO
To you, Antonio,
I owe the most in money and in love,
And from your love I have a warranty
To unburden all my plots and purposes
How to get clear of all the debts I owe. (1.1.137-141)
Bassanio says he's sharing with Antonio because they're friends, but he makes explicit that he owes Antonio the most in "money and love." (It turns out that Antonio has been very generous with Bassanio, who has a hard time keeping his finances in order.) This is our first hint that friendship might mean a different thing for Bassanio than it does for Antonio. Bassanio might just be working on Antonio's affection in order to keep his purse strings open.
Quote #3
ANTONIO
I pray you, good Bassanio, let me know it;
And if it stand, as you yourself still do,
Within the eye of honor, be assured
My purse, my person, my extremest means
Lie all unlocked to your occasions. (1.1.142-146)
Antonio is willing to do anything to help his friend, including loaning him the money to woo Portia. What's interesting is that Antonio says that it's not just his "purse" (wallet) that's "unlock'd" for Bassanio's use; he is also making his entire "person" available to his friend, which may suggest a sexual relationship.