Complex sentence: Their relationship never lasts for more than a single night until the finale of the series, "The Last One", in which Phoebe drives Ross to the wrong airport, before causing a diversion, giving them time to get to the other airport.
Split into simpler sentences: Their relationship never lasts for more than a single night until the finale of the series, "The Last One". In which Phoebe drives Ross to the wrong airport, before causing a diversion, so they could get back to the other airport.