I am 48 and single. I was previously married for 18 years and divorced. I now receive SSI benefits due to seizures and some other things. I would like to know if I MUST report to Social Security when my ex is of retirement age and how I can find out what my benefit would be from his work record so I will know (kind of) what my benefit would be.
Yes, as a condition for receiving Supplemental Security Income (SSI) payments, you are required to file for all Social Security benefits for which you are eligible. SSI is a needs based benefit intended as a last resort source of income for disabled, blind, and aged (i.e. 65 or older) individuals with little or no means of self-support (https://www.ssa.gov/ssi/).
As long as your ex is living and you remain unmarried, you could first qualify for divorced spousal benefits when both of you are at least age 62. When you become eligible, you should be able to find out how much your benefit rate will be by contacting Social Security.