"he doesn't know how long it'll be for" Well it will be as long as YOU determine, not him. He thinks this is within his power - ie K will just accept me back if I decide to. He thinks he is IT.
It's your job to show him/yourself/ the world that you will not sit around waiting for him. That's for you and your strength.
Either it will be permanent or YOU will decide that he has done the required work, dropped OW and shows true commitment to the M.
Tell him if he's coming round to see the kids that he lets you know in advance as you have things that you will do whilst he takes care of the kids. Even if you get in the car and sit in a car park. Get dressed up to go and sit in the carpark though!
There is no need for any 'talk' - the cards are on the table from both parties. You both have things to do; he has to grow up and you have to recognise how strong and great you are and that you don't need an abuser in your life.
Time to be a bit selfish Kirsty. The way forward is to concentrate on you. it will be easier now he's not in the house. I know that's a rubbish thing to go through, but I think it's better for the LBS mental health.