What does Sean explain to Frannie about the bridges and what they mean for his ability to talk to hearing girls?

Sean tries to explain that the bridges he'd talked about earlier wasn't just a bridge to the other side of the highway. He says that he considers hearing girls as being a part of the world that is shut off from him - something unobtainable. Sean says that Frannie already has both the hearing world and the deaf world and that he's envious.