Cars are about how we "move" through our world. Theoretically, it's best to be driving the car, not letting someone else drive it or being in the back seat, etc. :-)

The ex- and the ashes make sense if you think about it; the ashes of your time together, it's over. But sounds like you're still letting your time with him influence your moving forward in your own life? You're still trying to "prove" something (who has the most ashes, who got the better deal, is more at fault for the breakup?)? Maybe you've been wishing lately that you were still together or that you'd done something differently, etc.?

Bodies of water are usually "emotions"/consciousness so that you're over/falling into the ocean makes sense to me too.