I second PPs advice to see a solicitor and work out exactly where you stand before (1) making any changes or (2) making him aware.
He might leave temporarily but I doubt he would stay away until things were sorted
One thing it's very important to keep in mind when you're thinking through the practical implications for this and sorting everything out is that it's very easy to slip into having to sort out his side of it too, especially if you've been doing the organising and planning for both of you up until now.
Try not to think too much about what he might want. Protect yourself and your DC, but what he thinks is the best solution will be the best solution for him.
One of the reasons I felt I couldn't get my ex out is because "well, I have nowhere else to go" and "you're heartless", etc meant that I saw his problem as my problem. I felt like I couldn't actually get him out until I'd found him somewhere else to live, sorted out how he was going to pay for it and organised it all for him, because he continually refused to budge until I had. His view was that if I wanted him out, why should he have to organise it?
So my advice is that when you're organising everything, try to keep in mind whether each problem you're solving is for the DC's/your benefit or whether you're still inadvertently taking on his problems as your own.
Also be firm, and don't listen to the emotional manipulation bullshit he tries - keep telling yourself that he doesn't believe it himself - making you feel guilty and uncaring is just a ploy to get you to change your mind. I've wasted so much of my life staying with people against my better judgement (across several relationships!) because I felt so guilty and was so concerned about their needs/wants despite not being happy myself. Luckily I finally twigged, but I regret wasting so much of my own and DC's time before I realised that gaslighting was a thing.
It might help to write a list of the reasons you're doing this, or the things you're looking forward to when he's gone (or both!) to help keep your focus when things start to look impossible. Which they will - you just have to push through it and remember why you're doing this.