If you were still married as of December 31, your only filing options (since you said you do not have children) would be Married Filing Jointly or Married Filing Separately. Generally, in this situation, people will file as Married Filing Separately. In order to file as Head of Household, you would have to maintain a home for a qualifying child or qualifying relative.
When you file as Married Filing Separately, you will still need to enter his name and Social Security number on your return when asked or you will need to print and mail (if you do not have it and cannot get his SSN) with an explanation as to why you were not able to provide his SSN.
I understand the Married Filing Separately, but what do I enter in the Community Property Income Adjustments when I have no knowledge of what he earned in 2017? Do I leave it blank?
If there was no community income in 2017 then you might be able to disregarded. See IRS Pub 555 page 7
<a rel="nofollow" target="_blank" href="https://www.irs.gov/pub/irs-pdf/p555.pdf">https://www.irs.gov/pub/irs-pdf/p555.pdf</a>
You might want to consult a tax professional in your area that deals with divorce/separation and community property law in your state.