IS THIS TRUE?  'If legally married 2018 and LIVED TOGETHER AT ANY TIME DURING THE LAST SIX MONTHS OF THE YEAR' ....       Must live together to file Jointly or Separately?   
This Forum has has never stated that before when answering about criteria for Jointly or Separately.

What that means is if you lived together at any time during the last six months of the tax year, your only choices are to file married filing jointly or married filing separately.  NOT Head of Household.  if you lived with your spouse for any part of the last six months of 2018 you cannot file as Head of Household.

It does not mean you cannot file MFS or MFJ if you did not live together. You misunderstood.

Wasn't thinking about Head of Household.  Thank you for clarifying!

Hope that helped!

The W-4 you gave your employer does not dictate how you file your tax return--it just tells your employer how much tx to withhold.  Now that you are married, you have two filing choices:

If you were legally married at the end of 2018 your filing choices are married filing jointly or married filing separately.

Married Filing Jointly is usually better, even if one spouse had little or no income. When you file a joint return, you and your spouse will get the married filing jointly standard deduction of $24,000 (+$1300 for each spouse 65 or older)  You are eligible for more credits including education credits, earned income credit, child and dependent care credit, and a larger income limit to receive the child tax credit. 

If you choose to file married filing separately, both spouses have to file the same way—either you both itemize or you both use standard deduction. Your tax rate will be higher than on a joint return. Some of the special rules for filing separately include: you cannot get earned income credit, education credits, adoption credits, or deductions for student loan interest. A higher percent of your Social Security benefits may be taxable.  In many cases you will not be able to take the child and dependent care credit. The amount you can contribute to a retirement account will be affected. If you live in a community property state, you will be required to provide additional information regarding your spouse’s income. ( Community property states:  AZ, CA, ID, LA, NV, NM, TX, WA, WI) If  you are using online TurboTax to prepare your returns, you will need to prepare two separate returns and pay twice.

https://ttlc.intuit.com/questions/1894449-married-filing-jointly-vs-married-filing-separately

https://ttlc.intuit.com/questions/1901162-married-filing-separately-in-community-property-states

https://ttlc.intuit.com/questions/1894449-is-it-better-for-a-married-couple-to-file-jointly-or-separ...

Best wishes!

How how I change my status from say divorced/ separated back to single? I never been married

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@alishasells wrote:

How how I change my status from say divorced/ separated back to single? I never been married

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In you have Not filed the 2019 tax return, then click on My Info on the left side of the program screen.  Edit your filing status and change to Single.