What do I do if I don’t have my spouses social security number?

If you can’t get it from a previous return you can mail your return and write “refused” in place of the social security number. Enclose a statement saying he refused to give it to you along with his name, address and phone number if available. 

@michelle_duarte presumably you are filing Married- Filing Separate.  You just need to mail in the return. 

You can not file Married - Filing Joint. 

Are you living with this spouse and are you on Social Security? if yes to both, you must check the box to ensure that 85% of your social security is automatically subject to tax.