Read this: https://www.churchofjesuschrist.org/study/general-conference/2007/04/divorce?lang=eng

And then search the internet for other teachings on marriage and divorce from the Church. Read them all. Prayerfully and humbly do so.

To appreciate and understand the Church's position you must also understand the need for ongoing revelation. You must also understand that the standards and laws God has held his people to have varied "because of the hardness of their hearts." For marriage, and for a whole host of other things various practices during Adam's time were not the same as Moses's time and not the same as in the New Testament. Some standards and policies during Jesus's time were not the same as after his ascension in to heaven. Ask Peter about that.

God required different things at different times and for different peoples because of the "hardness of their hearts." It was the same God in all cases, but he was dealing with different people with different cultures and different levels of spirituality. Some times the law of Moses gets a bad rap, but it was from God. It wasn't the highest and holiest way to live, but it was good. God is able to work with anybody individually, and he's also able to work with various groups of people. God is wise beyond what we can comprehend.

How does the Church of Jesus Christ know the current standards and policies? (Answer: revelation)
Was ongoing revelation needed to run the Church by the Apostles after Jesus's ascension? (Look for the answer in the Bible, as taught by both Jesus and examples.)
Is ongoing revelation needed now? (Prayerfully study what the Church of Jesus Christ teaches about revelation and the need for revelation.)

If you do NOT actually want to know the answer to your question, then shame on you for asking. 😉