Great posts from you Toast. You're showing some great insights into yourself, which, do you know, just SHOWS that you are doing really really well with all of this. Your mind is working, and you are taking huge steps forward in your understanding and your abilities to break free.
What I and other posters are trying to do is help you choose your next step, I suppose - your next step among the many that you are taking by yourself - which is to keep him out of your home.
You say you think you're letting him in to show him that you're still coping - ok, it's an idea - but in fact all you're doing is letting him in to mark his territory still. You don't want to spend money on it - you don't want to change the decor because you don't want to imprint anything of you on it - all he will see is "ah yes, everything is still as I ordered it to be".
It's entirely up to you what you do in there now. If you want to change it, paint it, put up pictures/curtains, have throws, cushions, wall-hangings (portable so you can take them with you), then YOU CAN. This requires neither his permission nor his approval - in fact he doesn't need to even know, or see, what you are doing.
You know you respond to him as "child". Time to stop that now. Time to grow up and stay in "adult" mode when he's around - that means telling him to fuck off. Adults are allowed to say "fuck off" remember - use it on him! Mentally practise. In fact, have a post-it with "FUCK OFF H's NAME!" written on it and put it on the mirror or somewhere you see it every day. Put it on the front door! On the inside, so you see it before you open it.
Bolts on the external doors - stop him entering without your permission - then withdraw that permission and tell him to FUCK OFF.
I'm repeating myself deliberately, by the way
to try and embed the suggestion!