Not yet read through the entire thread, still catching up from this morning, but need to pop-up to say:
It’s not you, it’s him;
It’s not you, it’s her.
If you still have passcode for his smartphone, then trawl though settings menu to password options (you’ll need the passcode to open this option up) This will list all website accounts & passwords used from this current phone. Capture this information & keep safe.
Work through each option listed. You may come across known & unknown email accounts he uses & the associated passwords. Look out for financial accounts, hotels, car hire etc, anything where he may tread or stash monies. Could be you find the FB/social media account details you need etc to dip in for the detail you need to build up a dry powder store of evidence.
Providing he does not does twig that you have accessed his phone in any way, he won’t go through all the accounts to change the passwords.
When he is out & when you have the energy... get online to work your way through your lists, prioritising financial matters & capturing account details & get the information you need.
Go see solicitor at earliest opportunity.