Does watching lesbian videos during Ramadan diminish the reward for fasting?

Sins in general, and viewing forbidden things in particular, diminish the reward of fasting, and may even nullify it entirely, in accordance with the hadith (definition): "Many a fasting person gets nothing from his fasting except hunger, and many a person who prays at night gets nothing from his prayer except sleeplessness." Thus, the fasting person who does not guard his limbs from sins such as backbiting and slander will get nothing from his fasting but hunger and thirst, even if the obligation of making up the fast is waived for him.