The Jews asked Jesus, "Is it lawfull to divorce your wife for any reason?" Jesus told them, "Moses allowed for you to divorce because of your hard hearts" But it was not always so from the beginning......
Jesus then began to describe what you guys are talkig about,,,,If anyone divorces it's not okay for them to remarry, except to be reunited to their spouse. The exceptions are,,,,,
Adultery, death, and a non believing spouse leaving. Paul stated that If a non believing spouse can't live with the believer and leaves, then it's okay for the believer to remarry, because such a non believer is not bound by the covenant. However, the believer shouldn't leave the non believer if they can live together,,,(Paul says "how do you know you will not save them?"
The act of divorce is still not sin, but, marrying somone else is adultery if the conditions aren't met for divorce in the first place.
It's pretty simple.
Now as to whether someone who has divorced and remarried for another reason, is it adultery,,, I don't know. It seems that if you commited adultery by marrying another then that makes your first marriage potentialy void. And, makes your new marriage binding.
That's not a good way to look at it, as using sin, to make a new sin Okay. Obviously if you repented of your adultery, that's forgiven, and you must remain un married or return to your original spouse.
However, If your spouse left you and then remarried, that makes them an adulterer and you're free and clear with no repentence needed on your part.
It's simpler to me to remain married. What ever problems can be worked out. People are just lazy and selfish,,,,,,,,,,,,