This song is about a car journey and the couple inside the car are silent and not speaking. Something happened at the place they came from that made them feel like not talking. But this isn't just a sudden silence. A lot of the time at home they don't talk or discuss anything. Life is just routinue and it's time to end it. In the car the girl knows it's time to let go of their relationship but she hates having to do it because her feelings have not neccessarily stopped, she just knows their relationship isn't going anywhere so it has to finish. She knows how much it is going to hurt him which is why she REALLY doesn't want to do it.
But she knows she must.