This is where we have to imagine why and at what level exactly he is grieving. Antonio is not listed as present at the wedding where the plan to fake Hero's death was hatched. It may be fair to assume that he was informed of the plan off-stage, but Leonato is incredibly imprecise in his speech when it comes to talking about why he is distressed, instead talking about unhappiness and suffering in more general terms. Perhaps his choice of words is carefully considered so as not to outright lie to his brother. Additionally, old Antonio becomes violently angry in the ensuing confrontation with Claudio and Don Pedro and has to be verbally restrained and escorted, ironically, by Leonato, the man who could not say "patience." We can assume that Antonio has not yet been informed of the truth behind Hero's (non)death, and that he must be informed of it after leaving the scene here in order to fulfill his role in the finale. This means that Leonato is going through two levels of grief, feigned grief for the death of his daughter and very real grief for his damaged reputation. He also attempts to stir up a kind of grief-fueled anger in Antonio to help him confront Claudio and Don Pedro. The final point of his argument is a condemnation of being "so