This is where we have to imagine what exactly and at what level he is suffering. Antonio was not present at the wedding in which the plan to simulate Hero's death was conceived. He may have been informed of the plan behind the scenes, but Leonato is incredibly vague in his speech when it comes to talking about why he is grieving, instead talking about trouble and suffering in more general terms. Perhaps the choice of words was carefully considered so as not to outright lie to his brother. Furthermore, the elderly Antonio becomes violently agitated in the stall with Claudio and Don Pedro following him and needs to be verbally restrained and escorted away, ironically, by Leonato, the man who could not say “patience”. We can assume that Antonio has not yet been informed of the truth behind the Hero's (un)death, and must be after leaving the stage here to fulfill his role in the finale. This means that Leonato is going through two levels of grief, feigned grief over his daughter's death and real grief over his tarnished reputation. He is also attempting to inspire a kind of pain-fueled anger in Antonio to help him deal with Claudio and Don Pedro. The final point of his argument is the condemnation of being “like this”.