What causes Giovanni to sigh?

Homesickness.....

The young stranger, who was not unstudied in the great poem of his country, recollected that one of the ancestors of this family, and perhaps an occupant of this very mansion, had been pictured by Dante as a partaker of the immortal agonies of his Inferno. These reminiscences and associations, together with the tendency to heart-break natural to a young man for the first time out of his native sphere, caused Giovanni to sigh heavily, as he looked around the desolate and ill-furnished apartment.