If you have a sole prop or single member LLC, the only way to keep your business separate from your personal taxes for 2018, is to file as married filing separately. You list your business on schedule C and your personal stuff on the rest of the 1040, like always. Your personal and business taxes are combined as usual, but they are separate from your spouse's income. Your spouse files a separate return for their income and deductions. However, married filing separately often results in owing more taxes.
In Turbotax, for 2018 you could make a new online account, but you still have to keep your business and personal income on the same return. If you will be filing jointly with your spouse, you should also consider making a separate account instead of adding your spouse to your existing account. And if you will file married filing separately, your spouse will definitely need a separate account.
For the future, you could make an election to have your LLC taxed as an S-corp. This can't be retroactive to Jan 1, 2018, so you must file as a schedule C disregarded entity. You could make the election retroactive to Jan 1, 2019, if you file the election soon. As an S-corp, you prepare a form 1065 corporation return, which issues a K-1 to the owners, and the K-1 goes on your personal return. This requires purchase of a second Turbotax Business only program. Making the S-corp election may have significant consequences, especially regarding treatment of losses, and you should review your options with your accountant or tax professional first.
If you are trying to keep your money separate from your spouse in case of divorce or separation, simply filing as an S-corp may not do it. You should see a lawyer or accountant.
