I am trying to find out if I can deduct expenses even though the car I'm using is not under my name.
You can deduct Gas (and other Actual Expenses your written records prove, such as tolls and parking), but Not 'standard mileage' - which includes an allowance for depreciation. You can't take a deduction for depreciation on something you don't own. If you paid fiancee rent for use of vehicle, you could deduct that - but it would also be taxable income to recipient. Meals are generally Not deductible unless away from home overnight ...
You can deduct Gas (and other Actual Expenses your written records prove, such as tolls and parking), but Not 'standard mileage' - which includes an allowance for depreciation. You can't take a deduction for depreciation on something you don't own. If you paid fiancee rent for use of vehicle, you could deduct that - but it would also be taxable income to recipient. Meals are generally Not deductible unless away from home overnight ...
People (e.g. your fiance) who receive money for personal property (e.g. automobile) rental can take a direct deduction of expenses (e.g.IRS mileage rate) on form 1040. That is, she will owe no income tax if you rent the car from her at a rate of 54 cents per mile and you get the deduction on schedule C.