Even if you think he may be straight up with his finances, spending money on a forensic accountant IS money well spent.
In my experience with friends, it has covered itself tenfold with a few unexpected findings.
Secondly, I would 100% go along with his long term plans of maybe getting back together, living together in a vague sense, if it gets you a final financial order and divorce that you are happy with.
He is living in fairyland with his long term plans that he thinks he can set up just so.
He gets to head off and have his adventures of every kind, divorced and free, and you there to pick up again if and when he needs it.
If he gets a whiff that keeping you happy with a generous divorce, will provide him with a soft landing if required, he may well do it.
Box clever.
My good friends close friend found herself in this situation some years ago when her husband was found to be having a midlife crisis in the form of a younger colleague, who was on secondment from the US for 2 years.
He just needed to do this apparently. 🙄
She boxed clever, made the right noises, and got an excellent divorce, 75% of their lovely large home morgage free and the two teenager children full-time.
They both worked full-time in good careers.
The ink wasn't dry on the divorce and she put the house up for sale, got a great price, moved into the nearest city and bought a nice little house for herself and the teenagers, and a small two bed flat convenient for the university her children would be going to, which she rented out until they needed it.
She future proofed life for herself and the kids within 18 months.
His fling inevitably finished within the year,(he was dumped for another colleague) but there was no question of any soft landing, they had moved on.
He was a lost mess for a while and then met some woman 15 years younger, and had two under two in 3 years. What a joke.
Back with young children when his elder children were both enjoying university.
He admitted his huge regrets to his Ex, felt very sorry for himself.
His new wife took zero bullshit from him and he was run ragged in his 50's with young children and a busy career paying for it all.
She's single still living her best life, no interest in another relationship.
Playing the long game can really be advantageous.