Maybe he is waiting until ours have “flown the nest” - so be it; that would still be a more comfortable and convenient time to divorce than now
OP you actually don't really care if he divorced you/leaves you. You accept it as a possibility. Being ok with your husband having sex with another woman is one thing (I've known people who didn't mind this). Not caring if he divorced you, unless it's at an inconvenient time, is quite different.
I'm divorcing a man who views me like you do your husband. I'm not cheating on him although it would have helped our sexual incompatibility if I had. I can absolutely guarantee you that my divorce is 100x more inconvenient than yours would be because it involves visas, international moves and multiple languages, on top of a complex financial situation across countries, financial systems and languages. It's not comfortable and definitely not convenient. But knowing how little I'm actually worth as a person outside my monetary value to him (value = in terms of facilitating his career progression and keeping finances simple if we're together) is worth it.
My question is have you told him that if he divorced you when the kids have "flown the nest" (some only do that in their 30s!) then so be it? You just want him to stick around now, because it's financially inconvenient and the kids would grow up between two homes?
I'll admit that kids growing up between two homes isn't ideal. But it's better than growing up with parents who are play acting for years. And that's what you're doing. You're both pretending he's not cheating. If you both were actually were fine with it, then you'd tell him you're happy that he's found someone to give him whatever he's missing from you (we can't be everything to everyone) because your relationship feels good. And he would not dump her, he'd carry on with her relieved not to have to sneak around any more.
You're both playing at bring ok with non-monogamy, which is a set up I know can work well for some, except that actually neither of you are ok with it! And it's not really non-monogamy when it's not consensual - which he believes it's not. It's just cheating.
I do wonder if you'd have put up with this if your finances were separate, he didn't own a business and you didn't feel a financial gain from staying with him.