Matthew 5:28 is Jesus expanding the scope of sexual ethics in a culture that defined violation only by physical act. His point was not to make everyone guilty β it was to say that marriage is meant to involve the whole person, and that the eyes and heart belong to the covenant. For the spouse who has discovered their partner's pornography use, the theological harm names something they already feel: this was not just a private habit. It was a displacement.
Psalm 51 is David's prayer after sexual sin β and it is a model for both parties in this situation. The one who has broken trust can cry out "create in me a clean heart." The one who has been broken by trust can cry out too β from the same psalm β because the brokenness there is real from both sides. Romans 8:1 is the ground under both of them: no condemnation for those in Christ, including those who are trying to find the road back.
Commentary is from a charismatic Protestant perspective, drawing on KJV text and public-domain sources including Spurgeon, Andrew Murray, and Matthew Henry.