Alright so, yo, I don’t ship them romantically either, surprise surprise.
However, I do ship them as former (kind of) friends. Things fell apart a while ago during the Franco-Prussian war but, even then, things had never been great. War of Spanish succession, Franco-Spanish war, etc. Spain and France are still very good friends today, they have a lot of history together but, Prussia has sort of drifted out, ever since the Franco-Prussian war and WWI, the trio just hasn’t been… a trio.
They’ll call each other and drink together sometimes but, it’s just not the same. Prussia was always more of the type to hang out with other Germanics only, anyway. They were never that close in the first place.
France and Spain hang out all the time, Prussia generally stays at home by himself or hangs with Germany. Sometimes he’s with Austria, most of the time he’s by himself.