Wa-alaykum as-salamu wa-rahmatullah wa-barakatuh
In the Name of Allah, the All-Merciful, the Mercy-Giving
All praise is due to Allah. Peace and blessings be upon His Messenger Muhammad.
May Allah forgive you and grant your sincere repentance.
You did not say why you are not married. Marriage will solve your problem. But, anyhow, this compunction is a good sign. Never feel despaired of repentance. Allah (exalted is He) said,
“Say, [O Prophet]: O My servants! Those [of you] who have committed [sins in great] excess against their own souls, never despond of the mercy of God! For, indeed, God forgives sins, one and all. Indeed, it is He [alone] who is the All-Forgiving, the Mercy-Giving.” (Az-Zumar 39:53)
The door of repentance is always there, but you need to keep knocking sincerely until it is open.
Masturbation, by definition, is the stimulation or manipulation of one’s gentile to reach orgasm. Masturbation is prohibited as inferred from the Quranic verse “The ones, moreover, who are ever vigilant as to [the chastity of] their secret parts- except [in associating] with their wives, or [with] whomever their hands may rightfully possess, for, then, they are not blameworthy; but whoever seeks [a way] beyond this, then it is they who are the transgressors.” (Al-Mu’minun 23:5-7)
Part of sincere repentance is to quit all the practices that stimulate your desire, such as gazing at members of the opposite sex, watching explicit contents, etc.
You need also to keep your time busy with useful activities, because leisure time is a big opportunity for Satan to incite you for evil acts. Attend congregational prayers, find religious friends, stay away from the Internet as far as possible, try to memorize the Quran, practice fasting to break this appetite, try to serve your community through philanthropic activities, etc.
These are just examples of things that fill your time and keep you away from thinking about our appetite.
Allah (exalted is He) said:
“As to those who do not find [means] for marriage, let them keep themselves [pure and] chaste, until God enriches them from His bounty.” (An-Nur 24:33)
The Messenger of Allah (peace be upon him) said, “Whoever among you can afford to get married, let him do so, and whoever cannot afford it let him observe fasting, for it will be a restraint for him.” (Al-Bukhari and Muslim)
Pray to Allah to keep you chaste and to grant you a religious wife.
Almighty Allah knows best.