@Hummusandcrisps
You have the messages. Good! Be sure they're somewhere secure. And gather all the proof of finances you can get your hands on. Secure that away, too. Preferably out of the house. If it's on your computer, put it in a secure, locked document. But if you can at all get this information out of the house, or on a separate computer, that's the best. I've found that somehow men like your H begin to 'feel' there is a change in us. Maybe it's a 6th sense or maybe we show very subtle changes in attitude, changes we don't even notice in ourselves. But at any rate, suspicions can be aroused. This can be why it's important to get things out of the house.
I know you've said you haven't confided in anyone, and I understand why you haven't. But as your plans seem to be firming up, you may want to reconsider this. If you have ONE friend or relative, even if they're in the UK, that you have 1000% confidence in to keep their mouths shut you may want to tell them, if not everything, just 'enough'. That he's being emotionally abusive or similar. This person can not only be a rock to lean on, they can serve as a 'repository' for your documents.
You need to see a solicitor, pronto. Even if your plan isn't to leave for months, now is the time. You need to be educated as to what divorce will mean to you in the country you are now residing in. Take a snapshot of 'family finances' and all assets. Ask what and how divorces are processed (timelines, paperwork, etc) and what is 'usual' as far as financial settlements and child maintenance go. Forewarned is forearmed. If there is the least chance that you'll want to return to the UK, you also need to consult with a UK solicitor (by phone), or a local one with experience in international divorce/child issues.
It's not simply picking up and leaving. If you are in a Hague Convention country you cannot remove a child without permission from the other parent. So this brings me to another point. He said "She can keep the child, I just want to keep my money". So, how much is it worth to you to be rid of him and have sole custody of DS? I'm not saying he'd agree if you took a lower settlement or whatever in exchange for moving away or sole custody, but it's worth thinking about. However, you're a long way from that point now.
And please keep quiet! The main thing you have going for you now is the element of surprise. Throw the party, grin and chat to his bastard friends. Remember that you are now playing the role of a lifetime. The role of ignorant, unsuspecting wife. Play it to the hilt, you'll be glad you did.