Is it obligatory for a young man afflicted with diabetes, which affects his sexual health, to inform the girl's family or the girl herself of his illness before marriage?

The believer's duty during calamities is patience and seeking reward from Allah (احتساب), in order to attain great recompense. Allah Almighty says: "And We will surely test you with something of fear and hunger and a loss of wealth and lives and fruits, but give good tidings to the patient." Patience is obligatory, along with pursuing means of treatment. The most important of these is to frequently ask Allah for healing, and then to consult doctors. If the illness causes complete inability to engage in sexual intercourse, the wife must be informed. If the deficiency is normal, then informing her is not obligatory.