First of all, our hearts go out to you. Stumbling upon a betrayal of trust and fidelity is a painful experience, so we are praying for you and your husband.
What should you do? The first step would be to gently and firmly confront him. Galatians 6 says, “If someone is caught in a sin, you who are spiritual should restore him gently.” You caught your husband in his sin. Now, it’s time to restore him.
As you prepare for that conversation, pray for humility despite your hurt. Pray for a stubborn belief that his feelings in the moment are not as important as his future with you (and God!). Yes, he will probably not react perfectly, but God allowed you to find his stash for a reason. God wants to save your husband from the porn that will kill so many of the things he loves.
If he repents and apologizes to you and to God, forgive him. Tell him about the Jesus who died to save sexual sinners. Love him despite his sin, just like Jesus loves you despite yours. Continue to show him respect and kindness, even though he doesn’t deserve it.
If he doesn’t repent, pray for him and refuse to drop the issue. His soul is too valuable to do anything less.
As far as telling others, that is really a judgment call. I wouldn’t call the pastor, his best friend, or a counselor just because you found his porn. Instead, I would encourage him to take that step himself. Help him to see the value of a band of brothers to help him in the struggle. You can use CtC’s videos/resources to encourage him to do just that.
If he minimizes it and blows you off, tell him you need to get others involved. Show him 1 Corinthians 6:9-20 and insist that his soul is too important to you and you won’t let his pride be the cause of his condemnation. I hope it doesn’t get to this point, but what matters most is his eternity.
Blessings on your upcoming conversation. May the Holy Spirit guide you and give you the right words at the right time!