Act 4, Scene 1. What does Portia wants to find out by asking for the engagement ring from Bassanio?

The relationship between Antonio and Bassanio comes to the forefront in this section. Antonio can literally be seen as a lover of Bassanio, willing to die for him (4.1.260-274). This creates the conflict between Portia and Antonio, a conflict she is willing to test by demanding that Bassanio give her his ring. The fact that Bassanio parts with the ring for Antonio's sake, as does Graziano, implies that Bassanio chooses Antonio over Portia. This of course is unacceptable, as is seen in the next act where Portia severally chastises Bassanio for loving a man more than he loves her.