Retaliation is only going to put you in a worse spot in the long run.
The reason this is more of a problem is because he said his sex drive was low and because of that we would hardly have sex.
Ask him why he is using the application and if something is wrong in the relationship.
Porn vs Onlyfans, why is OnlyFans Cheating? Or maybe you want to find OnlyFans accounts in your area.