Hmmm... Not too sure what to make of this one.
She brought him along and spoke to him because she felt that he wouldn't be burdened by her and not hinder her plans (for possibly suicide), as he's apparently apathetic and distanced from other people - this is represented well by how they always sat some distance from each other when talking.
However, he seemingly does care, since he went out of his way to push the car around for her, and then revealed he never needed her assignment... So the visual representation kinda seems silly now, since they never sat closer to each other as he allowed her to open up more (perhaps it was to say he was listening, but he himself wasn't opening up?)...
But then again, he didn't do anything to stop her from disappearing, and seems to not be concerned with what actually happened, and leaves us with the mystery of what happened to her - which could be said to be a great way of conveying the questions left to survivors when someone does disappear like this... but he still doesn't care, so that message kinda falls flat.
It feels so disjointed, like it's trying to say something, but I have no idea what.
On another note, these two characters made me think of people who try so hard to make others think they're special. You're not deep or interesting because you forgoed having fun, or don't think the ocean is special. If anything, not being able to get meaning from the beauty of nature kinda shows a lack of critical thinking (ironic given that I'm perplexed by this story, but whatevs). But I suppose this style of thinking is a very teenage thing.