If you filed MFS for 2018 and your spouse did not also file MFS then he did not file. It is possible for you to amend the MFS return that you filed so that the two of you have a joint return for 2018.
https://ttlc.intuit.com/questions/1899507-how-do-i-amend-a-separate-return-to-married-filing-jointly
https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed?...
A 1040X cannot be e-filed. It must be printed and mailed. It will take about 4 months for the IRS to process an amended return. It is a good idea to use a mailing service that will track it, like UPS or certified mail, so you will know it was received.
Wait about 3 weeks from mailing and you can check the status of your amended return:
https://www.irs.gov/Filing/Individuals/Amended-Returns-(Form-1040-X)/Wheres-My-Amended-Return-1
https://www.irs.gov/filing/individuals/amended-returns-form-1040-x/amended-return-frequently-asked-q...
https://ttlc.intuit.com/questions/1908543-do-i-need-to-amend
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
