Stop asking him that question - he’s not told you the truth so far, and he isn’t going to tell you the truth either.
Don’t you think it’s mightily coincidental that he’s had a connection with someone else and now suddenly wants to be single?
I know you want this relationship to work, and to be honest hanging on like your are isn’t helping matters. The only chance I see is if he really understands what he stands to lose, but he’s never going to understand that for as long as your still there hanging on like you are doing. All that’s going to happen this way is that your going to be waiting for him to come back you whilst he is preparing to move away from you, and when he finally makes that move…..and he will, your going to feel immensely taken advantage of because he has and will have taken advantage of you, using you and keeping you hanging on while he’s busy setting up his new life.
Like I say your best chance is to make him see just what it is he has to lose. You tell him that his proposed arrangement is not enough for you and that you split up properly so that you can move on and find the happiness that you deserve. Tell him you’ve thought about it and realised your worth more than the crumbs he’s offering and that whilst it’s nice he wants to stay friends, your not looking for a friend, your looking for a partner who loves you in EVERY way, not just as a friend or even a best friend.
I know splitting properly seems like a gamble to you, but honestly it’s not. Either he’s going to wake up, get a shock and come to his senses (when he realises that you won’t fall for his frankly ridiculous idea being best friends and getting closer but not as a couple….I mean please 🙄) and realise what he’s got or, he will leave….like he was going to do anyway, the only difference being is that it’s going to happen a lot earlier, be a lot more difficult nothing like as easy as he had planned it to be.
Which would you rather OP - it’s the lesser of 2 evils…..
Would you rather he stayed with you stringing you along, pretending to be best friends and yet all the while he’s going after this other woman, making plans with her, getting his life sorted and setting things up with her until he’s ready to leave you properly? At which point he will leave you feeling used, devastated and heartbroken.
Or
Do you want to make this new life his dreaming of difficult for him, make him realise that cost of this new life is his lovely life that he had with you and the children. He’s going to have a much harder time going after this other woman when it’s complicated by splitting up with you, sorting living arrangements and looking after his own child and comforting her about the split. It’s hardly going to seem all romantic and meant to be when it all comes as such upheaval and such cost is it?!
Think carefully, put yourself first and don’t believe the crap that comes out of his mouth, any of it!!!