That question is aimed at people applying for an Unmarried Partner visa, where they have to show they have lived together in the same country for at least 24 consecutive months before applying and can prove it (tenancy agreements, utility bills, bank accounts etc.)
For a fiancé or spousal visa, you don't need to have lived together to qualify for the visa, so the question isn't relevant to you.
You can just put N/A.
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