Wait. Before you do anything you’ll likely regret, my advice would be to sit down and talk to him about the situation in a non-threatening, non accusatory fashion. Explain to him that you know he’s watching porn and ask him if you can watch it with him. Explain to him that you’re unsatisfied with the way things are currently and ask him if he has any ideas on how you two might spice up your sex life, and get things back on track… together.