You have correctly identified an interesting problem of the play and that is based around the character of Bassanio, who from this beginning scene of the play appears to be a heartless manipulator of Antonio's affections for him.
This scene introduces us to the world of wealthy merchants of Venice, who take great risks for their trade whilst feigning nonchalance about those risks. We can see this in Antonio's denial of worry about his ships. We can also see to that there is a crucial difference between the relationships of Antonio with his fellow merchants Salerio and Solanio. Although they clearly are friends, and feel it is their duty to cheer Antonio up, they excuse themselves when Bassanio arrives to do their own business. Clearly, their friendship has limits.
However, Antonio shows that he is willing to do anything for Bassanio - his relationship is one of true love. Surely we must be intended to read this line as being particularly suggestive: “My purse, my person, my extremest means / Lie all unlocked to your occasions”. The recent Al Pacino film version of this play makes the relationship between Antonio and Bassanio explicitly homosexual (shown by a kiss), and if you choose to read their relationship in this way, you can only go on to conclude that Bassanio is a bit of a spendthrift - he openly confesses to having wasted lots of Antonio's money, yet has the temerity to manipulate (for what else can we call it?) Antonio for money so that he can marry Portia. His motive he clearly states is to gain her wealth.
We can only defend Bassanio by his later actions of being wise enough to choose the right casket and having met his match in Portia, but still at the end of this initial scene he hardly wins our approval.