While Hal made it seem like Polly tried to kill herself over something that Jason did to her (which could still be true, we don't know yet) it's far more likely that Polly was sent away for as long as she was because her family discovered she was pregnant. Could this reveal about Polly also explain why Jason wanted to run away from home? Maybe Polly was sent away because her family worried that she would try to run off with her much-detested boyfriend.