He can not file a return that is joint without your signature. You cannot file as single, only married filing jointly or married filing separately. You can paper file your return so that it will be accepted. You should also notify the IRS that you were improperly filed as MFJ.
Any individual seeking legal advice for their own situation should retain their own legal counsel as this response provides information that is general in nature and not specific to any person's unique situation. Circular 230 Disclaimer - Advice given in this response cannot be used to eliminate penalties with the IRS or any other governmental agency.