“From what I understand, there is no Greek Orthodox RULE about divorce, and that while you state that marriage is an indissoluble union, there is not firm rule against divorce.”
There is a rule against divorce, but The Church, since at the latest the 7th century, probably a good deal earlier, has granted in certain circumstances a ecclesiastical divorce and allowed remarriage by economia. Second mariages are essentially penitential rites and third marriages are positively funereal. The reasoning is that it is better for people to repent and remarry than to “live in sin”.
BTW, only three marriages, no matter how they end. After that its off to the monastery!