Kitty - he's moved out and moved on sweetheart and so must you.
All you are going to elicit from him if you cry and get upset in front of him, is his pity at best, and that's the last thing you need.
As others have said, any 'honest' conversation you have is going to be one sided. You will be honest, he will lie and minimise, as he's been doing all along and it won't change anything in the long run anyway, just serve to upset you further and probably give you more questions than answers. Also you blaming yourself to a certain extent - 'I am messy, I didn't spend enough time with him' etc. etc. - all bollocks! Stop blaming yourself for his behaviour. He had an affair because he chose to have an affair, that's the bottom line.
Why is he 'calling in to see you tonight' For what possible purpose? To check on you, make sure you are 'ok'? Why? What good will it do? If you want to tell him you know about the affair, ok - do it in an email or a text or a brief call, but don't turn it into a discussion because you will only end up getting more upset.
You are far better of going no contact. Just claiming some time for yourself without him in it - to think, to spend some time completely away from him to sort our your feelings and emotions which are clearly all over the place at the moment.. Stay away from him and ask him to stay away from you. Tell him you are fine and there's no need for him to call in, and then starting setting about taking care of YOU.
He knows what he's missing. He's been with you for six years and he no longer wants to be with you. Harsh I know, but true. What he sees is a sad, desperate woman who would have him back at the drop of a hat. If you want him to see what he's missing then gather your self respect and resolve to get yourself in the best shape you can - emotionally, physically, logistically ... and then let the cheating bastard see what's he's missing, not the emotional wreck he's turned you into.
It sounds like you have an incredibly busy life with your mum, job, kids and grandkids and you don't need all this emotional turmoil on top of that. Take stock of what you have in your life right now (it sounds like a lot) and what you need to make things better for you and to put it bluntly, fuck him. He's clearly off doing his own thing with OW and has been for some time, so let him get on with it and put all your energy into yourself and those others in your life who haven't shat all over you as your husband has done.