In Othello, how does Cassio exploit the three women (Act 3, Scene 1)?
If your question refers only to Act 3, Scene 1 of Othello, Cassio doesn't "exploit" three women in the scene. He does wait outside Othello's residence hoping for a chance to speak to Desdemona. In that sense, he uses Emilia (Iago's wife and Desdemona's maid) to get to Desdemona, and he plans to "use" Desdemona to put in a good word for him with Othello so that he can get his position back. "Exploitation" is a rather strong word for Cassio's plan, but he is undeniably looking out for himself without considering how his talking to Desdemona secretly might hurt her relationship with her husband.
In other scenes, Cassio mentions his relationship with Bianca, and he certainly exploits her. In Act 4, Scene 1, Iago asks Cassio about his intentions regarding Bianca because she allegedly has been telling people that Cassio is going to marry her. Cassio's response to Iago is:
"I marry her! What? A customer! I prithee, bear some / charity to my wit; do not think it so unwholesome. Ha, / ha, ha!" (4.1.135-137).
It is obvious that he views Bianca as a passing fancy and as an inferior. This conversation, more than any other dialogue featuring Cassio, demonstrates that he is not wholly the thoughtful gentleman who he purports to be to Dedesdemona.