I imagine that general addiction indicators would apply. If they start off missing things because of the addiction. Isolating to indulge in the addiction. Angry, vehement, denials, instead of being willing to discuss the possibility when behaviors are questionable. The amount of time spent on the addiction is way out of proportion to other activities.
I have had to deal with alcoholics and coke addicted loved ones, I can’t speak to porn addiction. Maybe enter the Q into google and see if professional sites come up that can be more comprehensive than we are.
I hope this gets resolved satisfactorily.