It's a relationship that's gone stale and she's telling him that he needs to make up his damn mind - either stay and actually act like you care ("Take your seat..."), or leave. He's in between staying (sitting) and going (walking away) - he's just standing there. She's frustrated with the indecisiveness and is starting to move on already while they're still in the relationship.
I think the whole "beating up on yesterday" line is about him saying he regrets the time spent in the relationship. And the train is a physical representation of him leaving - he keeps thinking he'll wait until it's easy to "get off" - when the train stops. She's saying it's not going to be easy, basically telling him to take the leap, tuck and roll.
It's a relationship that's gone stale and she's telling him that he needs to make up his damn mind - either stay and actually act like you care ("Take your seat..."), or leave. He's in between staying (sitting) and going (walking away) - he's just standing there. She's frustrated with the indecisiveness and is starting to move on already while they're still in the relationship. I think the whole "beating up on yesterday" line is about him saying he regrets the time spent in the relationship. And the train is a physical representation of him leaving - he keeps thinking he'll wait until it's easy to "get off" - when the train stops. She's saying it's not going to be easy, basically telling him to take the leap, tuck and roll.