I'm addicted to masturbation, and I can't fast on Mondays and Thursdays.

Masturbation is an abominable act that must be abandoned, regardless of whether one is able to fast or not. One must fear Allah and strive against one's self, restraining it from what Allah has forbidden. One must also stay away from anything that arouses lust, such as forbidden gazing or thinking about it. A Muslim should supplicate to Allah to protect him from the evil of his own self. Fasting on Mondays and Thursdays carries great virtue.