Thank you to use Ancestris.
In a typical way, if you don't create a marriage event, the couple is not married.
You can also create a specific event and precise the type as Not married.
Some GEDCOM specialists will say that you can create a marriage event with the type "Not Married" (In my humble opinion, I don't like this solution, but this is a personal point of view).
For specific help with multiple marriages, please refer to the documentation for the specific editor you use :
https://docs.ancestris.org/books/user-guide/page/view-menu#bkmrk-%C3%89diteur-cygnusOr indicate the editor you use and what exactly you want to do.
Zurga