Although we don't know the details of Liesel's romantic feelings toward Rudy, which seem to be developing only as the story closes, there is still a romance going on. Since Rudy dies when he's fourteen, we don't get to know how this romance might have turned out.
Obviously, there's a big age difference here – ten or eleven years. Still, some readers find their relationship romantic. Some wonder if they get married after their reunion in 1945. What do you think?