Masetto is rather pissed off at Zerlina at the point, when right at their wedding party comes this nobleman and his servant, and the nobleman is flirting rather outrageously with the bride. Leporello knows what he's supposed to do: detain, get out of sight, and otherwise preoccupy the bridegroom while Giovanni tries to basically, score. Zerlina is flattered by Giovanni's attention, but Masetto is kind of like Jackie Gleason with his "Bang Zoom! to the Moon, Alice!", clearly adoring her while emitting empty threats.
I think Ottavio cares more about Anna than she does about him, but the details of their characters are rather lacking in the text than they are for other characters in the opera. They do have some gorgeous and very difficult arias though.