Are you scared of his reaction when you tell him OP? If so, then you may find it easier to move out on a day when he's not around OP, and just leave him a letter, perhaps you could book a day's holiday when you know he'll be at work and do it then? Do you have anywhere at work where you can take important papers and keep them there until after you've moved out? Do you perhaps have a friend who would be willing to store a few clothes for you? My friend did this, she kept putting a few clothes in a bag and popping them in her car, then would drop them off at her sisters, so gradually it got to a point where she didn't have quite so much to have to move. Maybe, depending on how many clothes you have, you could fill a couple of bin bags, and when/if he asks you what you're doing, you can just say you've had a good clear out, and are taking stuff you don't wear anymore to the charity shop.
You say you have grown children, is it likely that one of them would be willing to be there when you tell him, or would be willing to collect things after you've moved out, if you think he won't let you move back in?
How long do you think you will need to get yourself ready OP? Could you perhaps set yourself a target of say 3 months, and then aim for that?
Do you have somewhere in mind to go? If not, start looking, start getting stuff out of the house, particularly the paperwork that you will need. Get some legal advice, at which point you could check what help might be available to you, if he refuses to let you back in to get anything that may have been left behind. Also, if one of your kids would be prepared to help out, you could make sure they have a key to the property, so that they could collect things if needs be. If money's an issue, you could try Citizen's Advice, or look for a free 1/2 hour with a solicitor, but make sure you make a list of the things you want to know, before you go, so that you can make the most of the time.
You CAN do this OP!!