Part of Will deep down knows and therein lies the heartbreak and I will die on this hill.
We talk about how they wouldn't have had him give the painting or prompt Mike in the moment if they didn't want us to think it wouldn't have happened otherwise. But it is equally true that Will wouldn't have done it if he felt that it would happen without him.
Interrupting someone with "don't stop" is often a hard line to justify because it requires a bit of logic bending for why the character would feel the need to stop someone to tell them not to stop. But this is because Will, like us - part of him at least, did not trust that Mike would keep going without him.
The same is true in the van. He expected things to go wrong without him. Without something big, even. That's where the tears come from. And that is definitively what THIS look is:
He knows what he's responsible for. Deep down, somewhere. He wouldn't be so sad if he didn't think he'd given something up. He did this to himself and part of him knows it. Part of him knows that they wouldn't have.
