We lost the spark. How do I live with this guilt?

[MrBond]

"he'll just get annoyed that I'm making noise in the kitchen, because if he gets home late, he wants to go straight to sleep."

Stop walking on eggshells around him. Do what YOU want to do. Besides I'm sure there's a time you can cook something during a period he's awake. Lunch, breakfast, whatever.

"I texted him a simple message, "If you're stopping off at home first before we meet tonight can you please pick up the checkbook?" He said sure, so I just said thank you. That's simple enough, right?"

That's the right way.

"It is so difficult to figure out what will work, because he has been so stoic. No emotion, at all. Just monotonous and uninterested and flat. I can't break him yet."

Again, don't overthink. Start off small. Think about this way. He's built up this huge wall and you're like a big wave outside trying to batter it down. Each time you hit the wall, he fortifies it. Become more like a small stream. Instead of hitting his wall head-on, you find cracks and crevices to get through. Eventually you start to wear those down and so does the wall. Small actions with big impact. That's what you go for.