It seems Nathan is coming about as close to asking as a 7 year old will. I think it may be time to tell him. I know, it's going to break his heart. But, it's got to be done.
I like the idea of telling him Daddy didn't want to be married anymore works pretty well. True, but no real trashing. Someday, I think the kids will figure it all out. But they don't need it now.
I agree, Nathan is asking in the only way he knows how. Kids are pretty intuitive, they figure it out. About 8 months after my X moved out my daughter, who was 9 at the time, asked me if daddy was done divorcing me yet. She knew what was up. LOL
"You can't stop the waves, but you can learn to surf." Jon Kabat-Zinn