What kind of person is Cassio in Act 3? Has he changed?

We see Cassio as an upstanding and naive man, he plays by the book which makes him easy prey for the likes of Iago. Cassio seems to be one of the only "honest" ones in the play; he discloses his plans, his thoughts, and his concerns to Iago, omitting little or nothing. It is therefore ironic that he refers to Iago as "honest", since Iago is the complete opposite of everything Cassio is. By this point, the keyword "honest" has become very tainted by its over-association with Iago; it has no simple meaning anywhere in the play, and is definitely something to look out for.