Porn is short for pornography, which is video or print material that is intended to be viewed for sexual gratification.
Watching pornography according to the Bible is considered a sexual sin and considered the same as committing adultery.
Here are some scriptures to prove it:
“God’s will is for you to be holy, so stay away from all sexual sin. Then each of you will control his own body and live in holiness and honor— not in lustful passion like the pagans who do not know God and his ways.” 1. Thessalonians 4:3-5 NLT
“Give honor to marriage, and remain faithful to one another in marriage. God will surely judge people who are immoral and those who commit adultery.” Hebrews 13:4 NLT
And, Jesus made this very clear when He said;
“You have heard the commandment that says, ‘You must not commit adultery.’ But I say, anyone who even looks at a woman with lust has already committed adultery with her in his heart.” Matthew 5:27-28 NLT
Therefore, if your spouse is into porn, you have every right to leave such a person.
“I meant that you are not to associate with anyone who claims to be a believer yet indulges in sexual sin, or is greedy, or worships idols, or is abusive, or is a drunkard, or cheats people. Don’t even eat with such people.” 1. Corinthians 5:11