No. What you file at work (form W-4) is only an estimate for withholding purposes. It does not lock you in to how you have to file a tax time.
You cannot file married filing separately (MFS) because you were not married on 12-31-17. More importantly, you do not want to file MFS. Single is much better. If you have a dependent at home, you may qualify for Head of Household filing status, which is even better.
