namechange4life God I'm so sorry you're in this situation. What he's done to your family, your future (whatever happens he's changed everything) and your dreams (because of previous point) is deplorable.
I agree that you're doing the right thing in taking time to let it settle and see what you feel is right for you.
I live abroad (EU right now but hasn't always been). My POV comes from living outside the U.K. and getting divorced and also having grown up with parents split across countries.
I'm not saying divorce is the right thing for you, but in order for you to rule it out, you actually need to know exactly what it would mean. This has an extra relevance for you because your childhood memories are a child perspective, with attached child emotions, specific to your situation as a child with your specific set of parents. It's worth saying that it's different as an adult, different emotions and considerations. It would also not necessarily be the same for your child as it was for you. For a start I imagine that like me you may have had to rely on crackly phone calls and snail mail for contact - if any - with absent parent! And I am certain that you and DH are not replicas of your parents, even if you're similar in some ways.
You need to see a local lawyer specialising in international family law/divorce. You really need to know where you stand in terms of which marital regime (law) covers you. I'd actually do the same with a British lawyer from whichever British country you're from.
I KNOW that's hard to stomach, but honestly you cannot choose to stay with him if you aren't 100% clear about your fundamental rights in this situation.
You can also extend your month if you need a bit longer - I suspect it'll take you longer to figure out what you want to do because it requires you coming to terms with what he's done and what that really means for you. Please seek the legal advice (with a friend if that's possible for support and to help take notes - I recognise you may not have or want anybody to) asap though, because that is something certain in this mess. It gives you something stable to hold on to/reject while your emotions and thoughts are swimming all over the place.
And yes you need immediate and then regular STI testing. Condoms don't protect from all STIs. Sorry.
Please be really nice to yourself too. Anything that makes you feel good is something you should do. And that needs to guide how you handle the issue too. In even the most sympathetic way of viewing what your DH does, he's not put you near the top of his priorities. Make sure you're at the top of yours, not him.
As for being worried about what he'll do to himself, that's also not your problem. He's a husband and a father, he has to take responsibility for his actions - past, present and future and not lay them on you. This is a very typical emotional manipulation technique. Even just hinting that they would do something stupid if you don't have the response they want you to is typical.
And maybe, if you can, head back to the U.K. for a few weeks to give yourself some distance to think about it. You need to be able to trust him 100%. I have no advice on that because I wouldn't be able to trust him after this, nor would I forgive him for having multiple sex partners and then having sex with me.
I wish you the best. What he's done is truly awful.