Where are you getting that from?
Deuteronomy 24: 1-4
and
Jeremiah 3: 1-5
Better that divorce never happens; it is a sin. You might be able to make exceptions for adultery and make it not a sin for the wronged party, but that’s neither here nor there right now.
The point seems to be that once divorce is done, it’s done. I’d need to do more research and reading about remarrying your original partner if you DON’T remarry, but it seems to me that the opinion of the Lord is pretty clear here about going back to your first partner after remarriage.
But again, even that is a sin that can be forgiven; if it happened in my congregation (or remarriage or divorce in general) I would probably insist on public confession and absolution before allowing participation in the Lord’s Supper, but I would allow it.