In the case of Othello, love is presented as being intimately connected with jealousy. Iago may have whipped up Othello into a frenzy of paranoia and suspicion, but despite what he perceives as her adultery, Othello still loves Desdemona. Only he has a funny way of showing it, striking her in public and openly accusing her of being a false, promiscuous woman. There's clearly something not quite right about Othello's feelings for Desdemona, otherwise Iago wouldn't have found it so easy to convince him of her supposed infidelity.
Bianca's understanding of love is much the same. She too is convinced that she's being cheated on, in her case by Cassio. She believes that the handkerchief given to her by Cassio as a love-token was given to him by another woman. Bianca's intimate linkage of love—passionate love—with jealousy mirrors Othello's and likewise makes her vulnerable to Iago's devious machinations.
Iago is very much in control in this scene, and the action takes place on his terms. Playing upon the passions that he himself has never experienced, he's able to manipulate Othello and the other characters to his heart's content, jerking them around on a string like a master puppeteer.