B6 - he doesn't need an apartment to de-stress and find space to think. He needs an apartment so he can sleep with someone else. The same goes for the OW if she is still living with her spouse. Their desperation to be with each other is driving their every action right now. Rational arguments about finances and childcare are just puffs of hot air to someone in limerence. Stop trying to convince him to stay. In fact, tell him to go.
Your best course of action is to help him do it! Say goodbye with a wave and a knowing smile. If you google it, you'll find that limerent relationships tend to burn out once exposed to the mundanity of every day life. Bills and chores aren't sexy or exciting. Just leave him to his own destruction. You can be there to pick up the pieces if that's what you want, but you might find with enough time and space you realise you deserve someone better.
Don't expose yourself to his breakdown as it inevitably happens. It will only cause you more distress. Try to disconnect from him about everything except childcare and finances. Block him on social media and resist the urge to snoop. Don't be ashamed to talk about what's going on with your family and friends. Exposing the affair will either hasten its demise under the weight of shame, or force them to legitimise their relationship to try and prove they did nothing wrong.
Once he and OW have settled into 'domestic bliss', and the secrecy and fun of the affair wears off, he will realise that he has simply recreated the same problems with a different person. Because the problem was never you, it was him. I know all this advice probably seems harsh and scary. It is. But it's your best, if not only, chance of helping him realise what he is losing. He has to actually lose you, his kids, your shared life before he will learn to value it.
Finally, no contact isn't a tactic to get him back. It's to protect you and remove you from an abusive situation. He wants a divorce but seems to be on the fence? Push him off. Give him what he thinks he wants. The faster he experiences consequences for his actions, the faster he will wake up (if he's going to at all). Be polite and remote. You will not accept a demotion from wife to friend. How insulting would that be? You are a woman to be cherished, not merely tolerated.
