My 7yo asked why mommy lives in a different house

Not sure how to handle this one. He's asked a few times but yesterday it really hit different—he was sitting on my lap watching cartoons and just goes "why don't you and mommy live together anymore?"

I kept it simple, said sometimes grown-ups make different choices but we both love him very much. But man, that question is hitting me harder than I expected. Anyone else struggle with how to answer this without oversharing or making it about adult stuff they shouldn't know?