What is the ruling of the Sharia on a husband who travels far from his wife for a year, and who is unable to stop masturbating and unable to bring his wife to him?

Masturbation is forbidden and should only be performed out of pressing necessity. For example, if a person reaches a state where they are certain, or highly presume, that if they do not masturbate, they will commit zina (fornication/adultery). In this case, it falls under choosing the lesser of two evils. Mere distance from one's spouse does not permit masturbation unless it is accompanied by a real or highly probable fear of falling into zina. If a person fears that their desires will overcome them, they should fast, for fasting is a shield against such desires. Fasting curbs desire and mitigates the evil of semen, because sexual desire is dependent on the desire for food; it strengthens with the strength of eating and weakens with its weakness.