Oh, beware, my lord, of jealousy! It is the green-eyed monster which doth mock The meat it feeds on. That cuckold lives in bliss Who, certain of his fate, loves not his wronger, But, oh, what damned minutes tells
What dost thou mean?
Good name in man and woman, dear my lord, Is the immediate jewel of their souls. Who steals my purse steals trash. 'Tis something, nothing: 'Twas mine, ’tis his, and has been slave to thousands. But he that filches from me my good name
Iago is stating that Cassio is acting suspicious and he's doing something that he shouldn't be doing. This is so opener to the start of Othello's jealousy.
I’ll know thy thoughts.
Othello is wondering what Cassio is trying to imply.
You cannot, if my heart were in your hand, Nor shall not, whilst ’tis in my custody.
Iago is stating that he cannot ruin Cassios''s reputation. He is saying hurting Cassio would give me him gain. But through Iago's eyes it would benefit him.
Why, why is this? Think’st thou I’d make a life of jealousy, To follow still the changes of the mooWith fresh suspicions? No! To be once in doubt
Othello is saying that he will find out what Cassio is thinking.
I will not tell you becuase I have a heart. Basically I will never tell you
In this whole entire scene Iago is installing fear and insecurity into Othello, about Cassio's actions and how he might be doing something disrespectful to Othello. Which is making Othello very jealous indeed.