I think I understand that gut feeling you describe where his first voiced option is the OW and if it was over, that would NOT have come out his mouth. Instead, he could have said, "I'll check into where I can park my car overnight and live in it." If he were that respectful and considerate of you, You wouldn't have sent him packing, right?! So, yes I do understand that nagging question you're asking, "is it still going on?"
On the other hand, having a WH who also clings to rug-sweeping and passive-aggressive digs, it could also be true that it IS over, and it was just a dig to hurt you in a tender spot that you react to quickly and easily with him.
Let's face it though, once we choose to move on and push them away, there WILL eventually BE a OW. That is the reality, and you already noted that you recognize you have no control over that choice he makes.
Here's where I would focus less on the words coming out of his mouth (bait) and more on what he actually does. They lie. That's why we hurt so badly. Accepting that we will likely never really know the whole truth is very difficult. There is no justice in our suffering, is there? If when he leaves he goes to the OW... we'll, THEN, you know. Why stress now?
Hang in there!