My husband and I live in separate houses, with separate expenses, why would my standard tax deduction affect his tax return?

[MinhT1]

If you are married but file separately, then both spouses must either use the standard deduction, or both must use itemized deductions.

This means that if one spouse takes itemized deductions, then the other spouse must also take itemized deductions, even if their itemized deductions total less than the standard deduction.