My sister met her now-husband ten years ago. At the time, he was a heavy smoker and it was a deal-breaker for her so he quit and they moved in together, subsequently got married and had children.
She got Covid quite early on in the pandemic and completely lost her sense of taste and smell.
The last few times I’ve visited their home, i smelled cigarettes. Today, I bumped into my BIL and his car was reeking of cigarettes so it’s clear to me that he’s taken up smoking again because my sister can’t detect it.
Her reason for not wanting to share a house with a smoker was a mix of hating the smell, health concerns, and not wanting to raise children in a smoking home. Obviously, the smell won’t bother her now but the other issues remain.
So, in my shoes, would you tell her or mind your own business?