Porn can strain a relationship through secrecy, mismatched desire, and broken agreements. The repair is honesty plus a real stop plan, not a promise with no tools.
Partners usually get hurt by secrecy and comparison, not by the existence of adult content in the abstract. If you agreed to stop and kept going, that is a trust problem. If sex has gone quiet because the screen is easier, that is a desire problem. Both are common search reasons behind “can porn ruin a relationship.”
If you are quitting for the relationship, the other person needs to see behaviour, not speeches. A visible streak, a blocked phone, and fewer late nights with a locked door are more convincing than “I’ll try harder.”