Is "That changes nothing between us." acceptable?
Yes. I used it.
I wrote: "That still doesn't change anything between us."
Marked wrong, is it?
I did the same thing. I thought that's what the "doch" was for.
thanks for this link! I'm having loads of trouble with the particles.
Does "das" mean also this? or only that?
Just that. To say this you would say dies or diese.