First of all, when one has a sexual urge, it helps to thank God for this wonderful gift of sexuality. Too often we turn the urges into a negative thing. There’s nothing negative about them. Second, recognizing that this is a gift from God helps you also recognize who is to be the recipient…your spouse. Would you give this gift to another other than the one you join in sacramental marriage? Of course not. Would God want you to give this gift to yourself?
Even before Christ came along, it was considered exemplary to live a chaste life. Anne Catherine Emmerich in her visions of Mary’s ancestors described a people who put a great value on chastity, even for married people.
Now, some guys develop a habit early in life before they even know what sex is all about. As they can become adults, it’s hard to break this habit. In a case like that, the sin would likely be considered veniel. Then, too, often times the act becomes a security measure, especially if the boy comes from a difficult or hightly stressed family life. In a case like that, the act may have very little to do with sexual gratification as it does with self-affirmation. The problem is, as the person becomes an adult and realizes the what sex is for…he may tend to start linking impure fantasies to this act. That would lead to a greater propensity to start including pornography.
For myself, who believes and greatly appreciates the beauty of human sexuality between married couples, it would be a mortal sin.
I think it has to do with your level of conversion. Not that you should use that as an excuse. One should always strive for perfection knowing full well it will never be obtained.
