It is always sin, (either mortal or venial depending on the cirucumstances). With or without porn, the sin still exists. (porn would simply be adding on). It is a misuse of a gift of God, (sexual pleasure), which is ordered to the proper end of unitive and procreative love between men and women in marriage.
The good news is, like with all other sin, a firm resolve, prayer, repentance and contrition can bring about change, and even restore the charity (love/agape/caritas), that is lost in the commission of sinful acts. In fact, the desire to do it will diminish and finally pass altogether. It seems inconceivable while under the hold of the sin, but with a sincere heart, this will pass, as all evil, as Christ is stronger than the demons.
Looking to lessen the sin by rationalization, is not repentance. It is instead the force which perpetuates sin. So rather than say, "well if I do this or do that is it still sin?", (the essence of rationalization, and the show of desire to go on sinning), you should instead ask, "what is my sexual desire properly ordered for? What is God's will for me?" And then, with prayer move in the direction of God's answer, the best you can with God's help, perhaps through an accountability partner of some kind (if you're protestant or secular). (a priest, if you're Catholic), and sooner that you could probably even imagine, the desire will lessen, and then fade away. Gone.
Sexual immorality is the most common sin of human persons. It violates several commandments:
It can be idolatry
It dishonors one's father and mother
It is adultery, obviously for the married, but for the unmarried as well, as all other vocations are called to chastity. Without the unitive and procreative aspects of sex, there is a violation of our state of chastity.
It is quite often covetous
We are all sinners. Sin is an ailment. Jesus is the physician, and His church is the hospital. Prayer is the medicine prescribed.
I'll pray for you. Please pray for me as well.
A brief look at offenses against chastity from the Catechism:
Offenses against chastity
2351 Lust is disordered desire for or inordinate enjoyment of sexual pleasure. Sexual pleasure is morally disordered when sought for itself, isolated from its procreative and unitive purposes.
2352 By masturbation is to be understood the deliberate stimulation of the genital organs in order to derive sexual pleasure. "Both the Magisterium of the Church, in the course of a constant tradition, and the moral sense of the faithful have been in no doubt and have firmly maintained that masturbation is an intrinsically and gravely disordered action."138 "The deliberate use of the sexual faculty, for whatever reason, outside of marriage is essentially contrary to its purpose." For here sexual pleasure is sought outside of "the sexual relationship which is demanded by the moral order and in which the total meaning of mutual self-giving and human procreation in the context of true love is achieved."139
To form an equitable judgment about the subjects' moral responsibility and to guide pastoral action, one must take into account the affective immaturity, force of acquired habit, conditions of anxiety or other psychological or social factors that lessen, if not even reduce to a minimum, moral culpability.
2353 Fornication is carnal union between an unmarried man and an unmarried woman. It is gravely contrary to the dignity of persons and of human sexuality which is naturally ordered to the good of spouses and the generation and education of children. Moreover, it is a grave scandal when there is corruption of the young.
2354 Pornography consists in removing real or simulated sexual acts from the intimacy of the partners, in order to display them deliberately to third parties. It offends against chastity because it perverts the conjugal act, the intimate giving of spouses to each other. It does grave injury to the dignity of its participants (actors, vendors, the public), since each one becomes an object of base pleasure and illicit profit for others. It immerses all who are involved in the illusion of a fantasy world. It is a grave offense. Civil authorities should prevent the production and distribution of pornographic materials.
2355 Prostitution does injury to the dignity of the person who engages in it, reducing the person to an instrument of sexual pleasure. The one who pays sins gravely against himself: he violates the chastity to which his Baptism pledged him and defiles his body, the temple of the Holy Spirit.140 Prostitution is a social scourge. It usually involves women, but also men, children, and adolescents (The latter two cases involve the added sin of scandal.). While it is always gravely sinful to engage in prostitution, the imputability of the offense can be attenuated by destitution, blackmail, or social pressure.
2356 Rape is the forcible violation of the sexual intimacy of another person. It does injury to justice and charity. Rape deeply wounds the respect, freedom, and physical and moral integrity to which every person has a right. It causes grave damage that can mark the victim for life. It is always an intrinsically evil act. Graver still is the rape of children committed by parents (incest) or those responsible for the education of the children entrusted to them.
2357 Homosexuality refers to relations between men or between women who experience an exclusive or predominant sexual attraction toward persons of the same sex. It has taken a great variety of forms through the centuries and in different cultures. Its psychological genesis remains largely unexplained. Basing itself on Sacred Scripture, which presents homosexual acts as acts of grave depravity,141 tradition has always declared that "homosexual acts are intrinsically disordered."142 They are contrary to the natural law. They close the sexual act to the gift of life. They do not proceed from a genuine affective and sexual complementarity. Under no circumstances can they be approved.
2358 The number of men and women who have deep-seated homosexual tendencies is not negligible. This inclination, which is objectively disordered, constitutes for most of them a trial. They must be accepted with respect, compassion, and sensitivity. Every sign of unjust discrimination in their regard should be avoided. These persons are called to fulfill God's will in their lives and, if they are Christians, to unite to the sacrifice of the Lord's Cross the difficulties they may encounter from their condition.
2359 Homosexual persons are called to chastity. By the virtues of self-mastery that teach them inner freedom, at times by the support of disinterested friendship, by prayer and sacramental grace, they can and should gradually and resolutely approach Christian perfection.
