I'm not sure that giving him a "punishment" is the solution to your problem. If you don't give him sex, baka mas lalo pa magworsen yung addiction nya sa porn, and in the end, you two would have grown farther apart.
I think first, you really need to get an honest answer from him as to why he's doing it. Only then can you move forward to actually find a solution to the problem. Pero if you're not really looking for a solution but would just want to get even and "punish" him, then I guess no sex and no talk is good enough. Just make sure that the punishment is actually making HIM feel bad, not you.