I haven't read previous threads so not sure if something is going on there but what bluntness said seems fair.
You are comparing two unfavourable situations to a preferable one...but the preferable one doesn't exist! So you are staying in a bad situation waiting for this other one to appear. It sounds like it isn't going to appear. So take some control.
The current compromise you've found in your relationships suits some people, including your DH. It doesn't suit you. You may motivate your DH to move back in, if he truly believes that things will end if he doesn't, but:
a) it's been like this for a long time, he may think you're bluffing and just make the right noises. Empty promises, etc.
b) if he moved back in, it sounds like he would be doing it pretty reluctantly...how long will that last?
I think the advice of moving on is spot on. Sounds like you've explored what you can, put what you can into it, and for whatever reason he isn't motivated to do the same. Or he just doesn't want what you want, and knows that it won't work for these reasons. I'm sure he cares about you and the DC, so it's in his interest that he has tried to keep things moving along for as long as possible without having to change anything.
The unknown is psychologically much more difficult than a difficult or "bad" outcome. Personally I find a situation out of my control induces higher levels of anxiety than a less preferable situation but one over which I have some control.
This also applies to the kids. I imagine they are struggling with not really knowing exactly what is going on with the situation?
Good luck. If you aren't ready yet, I think as a minimum now would be a good time to give yourself some hard timelines. If you aren't ready, write down in X many months time what outcomes you want to have achieved, and what will happen if they haven't been achieved. Don't tell him. Don't spend every day thinking about it. Get to do that day, and act accordingly. I don't think this is a wise move, seeing as it's already been going on for a long time (better advice if it had only been a few months so far), but it is an intermediate option.