He marry, or at least select a bride

Ultimately, it was Catherine who forced a decision on him. Stanislaus received an official message from the Russian foreign ministry in St. Petersburg telling him that it was essential that, before the opening of the election Diet, he marry, or at least select a bride. He realized that the message must have been approved by Catherine. Understanding, finally, that he had lost the woman he loved, he surrendered and signed a declaration that he would never marry anyone other than a Roman Catholic, and then only with the approval of the Polish Diet.

Is the tense in red subjuntive for the past? Thanks!