Is it permissible to masturbate if one's wife refuses intimacy and one cannot endure abstaining from intercourse, especially in a country where it is easy to fall into sin?

If you are capable of marrying another woman, then hasten to protect your chastity, and be just between your two wives. If you are not capable, then strive to rectify your wife through admonition. You must be patient and chaste if she does not return to obedience or if she does not keep you chaste. It is not permissible for you to masturbate except out of necessity. You must fast, guard your hearing and sight, avoid places of temptation and passion-arousing stimuli, seek Allah's help and rely upon Him. Occupy your time with what benefits you in your religion and your worldly life, and be keen on the company of the righteous. And you must supplicate frequently.