We are already in an "unwinnable" war! Unless we give more to Ukraine, quickly, this will go on until the entire country is flattened.
Our fear of enraging Putin is costing lives every day. Putin's threats are just that: threats. I've read many expert opinions who say there is no way he's putting nuclear weapons in Belarus--he's bluffing.
This is not to say it's problematic. But nuclear weapons require maintenance--and we've already seen how the Russian's weaponry has been maintained--it hasn't. Their stockpiles are old and poorly maintained. I don't think there is any reason to believe his nuclear capabilities are any better.
We should be cautious, of course. But not talking to Russia at this point means not allowing lies and propaganda to give us false hope. All we need to do is see what Putin is actually doing. That tells us everything we need to know.
My guess: Putin doesn't want us to share information because then his bluffs won't work.