What of the person who went forward in church to receive Christ as his Savior; yet that person has no apparent change in his life or thinking. Since his teen years he has believed that nature proves there is a God. He believes that Christ's blood pays for his sins. He talks of the better life that awaits him after death.
Such a person, according to Scripture, is still spiritually dead, unregenerate, self-deceived and remains under the wrath and condemnation of God. I'm afraid there are thousands upon thousands out there who are even communicant members of churches.
Why doesn't the Holy Spirit create a change is his desire to serve the Lord in the ways of holiness? Why is the person seemingly addicted to porn and trying to keep his wrongdoing from those who would claim it is sin?
1. Why should the Holy Spirit regenerate his dead soul? God is under no obligation to do so, right? Salvation is by grace alone according to His determinate counsel and infinite mercy. This is a question that is best answered by Deut 29:29.

2. This person's sinful life is
natural; how one would expect an unregenerate man to live.
I don't believe that people don't struggle with sin, but I have trouble with an apparent lack of repulsion towards it. Yet can such a person be more interested in what others think of him rather than actually hating the sin itself? Does this person want the approval of men more than that of God?
Truly regenerate individuals do have a repulsion toward sin to one degree or another. We can't quantify the repulsion and shouldn't; that belongs to the Spirit. And we must allow that people who are regenerated don't become instant "saints" and perfectly holy. Sanctification is progressive in nature and it takes time, a lifetime for most of us, to even begin to make a dent in our transformation. There are those, however, who think they have already
arrived and are not bashful about telling you so. You can usually identify these people by their constant and almost immediate condemnation of everyone else, relegating nearly all to perdition because "they ain't saved". But back to a more biblical view, this person you are asking about obviously is living a life that is not consistent with one who professes to believe in Christ. Paul puts it this way:
Titus 1:15-16 (ASV) "To the pure all things are pure: but to them that are defiled and unbelieving nothing is pure; but both their mind and their conscience are defiled. They profess that they know God; but by their works they deny him, being abominable, and disobedient, and unto every good work reprobate."
Has anyone had some communication with this person to speak of these things to him? IF this person is a member of a church, then the elder(s) should be aware of this man's sinful lifestyle and take appropriate action to counsel and/or discipline him if necessary. Should this person be confronted with his sin(s) and the seriousness of it/them and refuse to repent, then at least if/until he repents of the sin(s), he must be considered an unbeliever. (1Cor 5:1ff)