It sounds like he's desperate for you to be his idea of happy. And talk it to death. If it were me, I would simply say "I love you but I don't want to talk about it right now". Then, I would repeat that as many times as needed.

Some people are dreamers and live in the future they create. And good for them...

Some people prefer the reliability of the here-and-now. And good for them, too...

Without one, the other isn't likely to happen. I see that as a positive thing.

I'm so SO sorry that this causes you such distress. He should be more compassionate about that...