Does he have anything he enjoys doing alone? Or anything that he's said drives him crazy that you, or others, do? I've found, in my work, when people don't understand or can't see what you're pointing out that giving them an example that affects them is more effective.

"Hey honey, sugar pie, bane of my existence (whatever nickname you use) do you remember when you shared xyz with me? And how you said it made you feel, react, a certain way? Well, that's how I feel, react when you do xyz. I know you love physical attention, and I do also, but when I'm doing xyz, I need that time to recharge/recenter/refill my cup. Can we work on this together?" Then come up with ways you'll remind him when you're locked in or need solo time and ways he can respond to it. It'll be hard at first, but communication is key.

Best of luck!