In Act II, Scene 8 of The Merchant of Venice, why does Salanio offer more evidence of Antonio's love for Bassanio?

Act II, Scene 8
SALANIO

I think he only loves the world for him.
I pray thee, let us go and find him out
And quicken his embraced heaviness
With some delight or other.

Act I, Scene 1
ANTONIO

In sooth, I know not why I am so sad:
It wearies me; you say it wearies you;
But how I caught it, found it, or came by it,
What stuff 'tis made of, whereof it is born,
I am to learn;
And such a want-wit sadness makes of me,
That I have much ado to know myself

ANTONIO

I hold the world but as the world, Gratiano;
A stage where every man must play a part,
And mine a sad one.

The conversation between Salarino and Salanio in Act II, Scene 1 of The Merchant of Venice in which Salanio offers more confirmation of Antonio's love for Bassanio reflects back to Antonio's play-opening speech in Act I, Scene 1. Here, Antonio starts the play out by saying, "I know not why I am sad." In the subsequent conversation between Antonio, Salarino and Salanio, Antonio denies that his sadness is related to business or to love sickness. The only clue we have as to Antonio's sadness, which Salanio refers back to in his remark "I think he only loves the world for him," is Antonio's declaration that the world is "A stage where every man must play a part."

What all this indicates is that in Act III, Scene 8, Salanio gives more evidence of Antonio's love for Bassanio in order to give us another clue to Antonio's psychology. After all, in Act I, Scene 3, we have just watched Antonio behave in a shocking and hateful manner toward Shylock after being so very loving, patient and kind to Bassanio. It might be suggested that Salanio's statement of Antonio's great love is meant to lead us to the conclusion that Antonio's sadness is the part he plays of denunciator (condemner) of Shylock the Jew, moneylender.