Is repeated sexual fantasy that leads to discharge considered a sin, especially with no intention of marriage, and is that considered Zina (fornication/adultery)?

Intentionally thinking about sexual intercourse and summoning related fantasies is not permissible. However, if thoughts and fantasies overwhelm one's mind without being summoned, there is no blame, but one must resist these thoughts and fantasies and not yield to them. The root of all corruption stems from neglecting stray thoughts and giving in to them. The most effective remedy for lust is marriage. If a woman fears falling into sin, marriage becomes obligatory for her if it is facilitated. If marriage is not possible, she must be patient and practice chastity. What helps her in this regard includes: lowering her gaze, closing the doors to temptation, staying away from everything that incites lust, strengthening her connection with Allah, associating with righteous women, occupying her time with beneficial activities, and persistently supplicating.