Like the Lady said, if it becomes an addiction it's sin. As to when does it become an addiction, it's when you cant let it go: Unless we forsake everyone and everything and our own life, we cant be His disciple.
"Nothing is evil in itself, but to him who esteems it ("Lovers of pleasure more than Lovers of God.") to him it is evil." "Whatever is not of faith is sin." In the case you find yourself addicted and think shamefully of yourself, rather "God be merciful to me a sinner," In this sense doesn't matter if its sin or not, as "Sin shall not have dominion over you for you are not under the law but under grace." "All manner of sin shall be forgiven unto man but rejecting the Holy Ghost shall not be forgiven to man." Have masturbated while praying in tongues: to release stress and verify wether it was possible to be considered not sin: not rejecting the Holy Spirit wile doing it. One of the few time there was no shame involved, I have struggled with addictions practically my whole life and could possibly be one of Paul's rivals as chief of sinners and compete with "not of works lest any man should boast." Our accomplishments are fitly rags so we don't think to highly of ourselves. But as single we are to aspire to love the Lord with our whole heart and not be distracted by the world, as opposed to married people who 'Seek the things of the world to please their mate." An expression of love in marriage; an opportunity to dye to our selfish nature and seek to please the Lord without distraction as single. "The time is short, it remains that they that have wives be as if they have none,"