I have been married 20 of the 25 years to my ex. He says, I cannot get any retirement because I remarried.

I think that your ex is confusing spousal support with asset division.  If you have a judgment from the court stating that you receive a percentage of the retirement from the ex, then you receive it whether you remarry or not.  You will need a QDRO (qualified domestic relations order) and possibly a Joinder in order to collect the funds.  An attorney usually prepares these documents.