Arguably, the moment of truth, or the epiphany, for Roderigo comes in Act V scene 1, when he is stabbed by Iago and he dies realising suddenly just how stupid and foolish he has been and how easily he has been used by Iago for his own purposes. Of course, at various stages in the play Iago has had to do some very fast talking with Roderigo to persuade him not to give up in his love for Desdemona, and he only manages to do this by telling him that her attraction to Othello is based on a lust that will pass. However, it is when Roderigo is stabbed by Iago that he realises just how he has been duped. Note what he says to Iago at this stage:
O damned Iago! O inhuman dog!
Clearly, this represents Roderigo's moment of truth where he is forced to see the reality of his relationship with Iago and, by consequence, just how much he has been manipulated by him, resulting in his death.