Obviously OP cannot ask the mum, but back in the beginning the ex would suddenly decide he'd stay at his mum's for the night.
Would a mum who covers for her son staying with an OW look taken aback about being told of the divorce? Maybe he never even told his mum that he'd left the family home overnights.
Everyone gets a different version of why he blew up his family precisely because it's not actually OP's fault at all. What he calls control actually made his married life quite pleasant so now he has to spread the misery around and make OP suffer too. It may be as straightforward as this.
Now that he's free to do things his way, the more often they go wrong, the more justified will OP's past "control" look. I think that's why he's stalling, so that he can blame OP for as long as possible while he tries to get his bearings. It's a good idea to get the addresses and everything separate asap.