And to be fair, your point ultimately boils down to distrust.
OK, possibly to a degree, but I think it was more that Stalin wanted the BBD (Bigger Better Deal, at least in his eyes), no matter where he got it.
And in all fairness I do believe Stalin knew that a confrontation with Germany was bound to happen, sooner or later.
As far as I remember the deal came to a halt because Poland didn't want to allow soviet troops passage through their territory as they feared they would never leave again. Also the UK and France feared that this would ultimately lead to an Soviet hegemony in the east which they certainly didn't wanted. So it came down to it that the western Allies, especially Poland, didn't trust the USSR. Given what happened in the Baltic after the occupation of Poland, I would say that that distrust was well founded.
Only after the negotiations were suspended to an undefined time the USSR and Germany made an effort to make negotiations of their own.
What Stalin really thought about all this is hard to say, while he probably expected that a war with Germany was bound to happen, he certainly didn't expected it to happen so soon.
Stalin actually had a tendency to have deluded views on many things. He for example believed a report during the Finnish war that the Finnish people were just about to start a communist revolution and help the red army in "liberating" the country. This of course was not true and should have been hard to believe anyway because the red army currently killed the fathers and sons of these very people who were supposed to help the red army.
Not the best basis for cooperation.
So what Stalin thought at any given time can be hard to comprehend, maybe he put up this whole thing with the Allies as a farce to get a better deal out of Germany, maybe he actually would have preferred to get the deal with the Allies and Germany was his second choice. Without hard evidence, that I am not aware of exists, it is really just speculation. But it can be said for certain that the Allies didn't accept the deal with the USSR because they just simply didn't trust them enough in the end.
As you say, the deal with the Western Allies was never going to happen because Poland (quite reasonably) wouldn't allow it. Britain and France had nothing really to offer Stalin - and certainly nothing Stalin would get excited about. But then along came Hitler with a tempting bag of goodies.....
I still think the most plausible reason for the deal with Hitler was that Stalin (again quite reasonably) thought of WWI and foresaw the Germans and Western Allies slaughtering each other to a standstill.
Ergo. The west (inc. Germany) is no longer a threat to the USSR and, if he wants to, Stalin can start dictating the terms of the NS Pact 2.0. The The straits would be high on the agenda no doubt.....
Stalin's nightmare was an Anti-Bolshevik crusade scenario with Germany, Britain, and France allied against him. In his deluded mind, Poland's objection to foreign troops was meaningless. He did not understand the role public opinion played in democracies, and that a 2nd Munich-like deal was politically impossible for Britain to contemplate.
It's odd that Stalin apparently believed Hitler would not break the Molotov-Ribbentrop Pact and attack him, in spite of Hitler having broken other treaties (and breaking many himself). Did Stalin make the mistake of believing his own propaganda?