What kind of person is Cassio in Act 4

I think Cassio doesn't change a whole lot in the play. By act 4, he is really still as confused as ever and being set up, by Iago, yet again. Iago calls Cassio in, while Othello hides; Iago speaks to Cassio of Bianca, but Othello, in his disturbed state, believes that Cassio is talking of Desdemona, which is the last "proof" he needs before declaring his wife guilty. Bianca comes in, and gives the handkerchief back to Cassio, since she swears she will have nothing to do with it. Poor Cassio is still the same guy, loyal to Othello but now embroiled further in a web of lies of Iago's making.