Matthew 5:31-32
“Furthermore it has been said, ‘Whoever divorces his wife, let him give her a certificate of divorce.’ But I say to you that whoever divorces his wife for any reason except sexual immorality causes her to commit adultery; and whoever marries a woman who is divorced commits adultery.”

Jesus really shook up everyone with these two sentences. It wasn’t contrary to the Law but rather enhanced it. Deuteronomy 24:1-4 explains the Law of Divorce.
Jesus’ teaching here seems directed at the woman – causes HER to commit adultery or if you marry HER you commit adultery.
According to the Law, only the man could get a divorce. God allowed this in the Law because of the people’s hard heart. Is divorce sin? Jesus certainly points to the fact that it leads to sin. It seems if you divorce you cannot remarry. And you violate the God basics of marriage “what God has joined together, let not man separate.”
Of course, many marriages are not godly joined together. Many marriages are born from lust, convenience, necessity, or economics.
This teaching also shows how your actions affect others!
Jesus also gives a reason to divorce as sexual immorality. This can range from fornication, adultery, homosexuality, or bestiality – I’m sure there are others. I might add that watching pornography while married is a sin because it leads to lust and lust leads to adultery in the heart and mind.
Someone that would commit a sexual sin while married is already not living a Godly life.
However, Jesus does not say you HAVE TO divorce because of it. Certainly, God would be pleased with repentance, salvation, and reconciliation.