I think this is supposed to explain the ending when she shoots him, which is his solution to death and alone-ness. It's the only way to finish without devaluing everything that came before, which makes death the solution.
I don't give a fuck about a bit of butter on her buns. We're dealing with larger issues here.
I'm waiting for the sequel. Last Tango 2. They end up getting bored with eachother, fighting over petty nonsense, mutually agreeing that some time apart would be a good idea, and eventually meeting other people.