While some have made the claim that there is more to the relationship between Bassanio and Antonio, I think it is more brotherly. A friendship. Quotes like this one,
"Commend me to your honorable wife:
Tell her the process of Antonio's end;
Say how I lov'd you, speak me fair in death;
And when the tale is told, bid her be judge
Whether Bassanio had not once a love."
(IV.i.273-278).

That Antonio says (when he thinks he is dying) shows the extend of their friendship. Antonio is showing the rivalry between who could love Bassanio more, between himself and Portia. In response, Bassanio says, ""I would lose all, ay, sacrifice them all / Here to this devil, to deliver you" (IV.i.286-287). And by all, he is referring to his wife whom he loves, "dearly."
"The Merchant of Venice" then portrays brotherly, familiar love as being as important as love between a man and a woman. However, after the ring incident, Portia scolds Bassanio and reminds him that a love between a husband and wife is more important than a friend. However, whether or not Antonio or Bassanio believe that is questionable by the actions and words that they have already said. Male-Male relationships in the play are more important to the two heroes than their wives. The wives who feel that try to change the minds of their husbands, but I don't think they ever succeeded.