People sometimes ask why the Bible is not more definite about the right to remarry after divorce for adultery. The answer is simple. In the Bible the right to divorce carries with it the right to remarry. The Fourth Century Latin Fathers tried to make this separation from bed and board. However, a dissolution divorce was the only kind known to the Jews.
Jesus did not give the faintest hint of anything else. It was the only kind known to the Greeks and Romans. The separation divorce was not invented by Latin monks until several centuries after Christ.
In OT times men were allowed to have multiple wives and concubines. Some of the greatest saints were born from these polygamous marriages. But with the NT law a man can have only one wife.
For the cause of all sexual sin Jesus approved the Jewish divorce that allowed remarriage.