Is a person who frequently engages in sexual intercourse, desires beautiful women, contemplates engaging in extramarital affairs, and is aroused by talk of the "fairer sex" considered to be among the category of people whom Allah Almighty referred to as having a "diseased heart"?

The strength of one's virility does not justify looking at foreign women. Rather, one must lower their gaze in response to Allah's command: "Tell the believing men to reduce [some] of their gaze and guard their private parts. That is purer for them. Indeed, Allah is Acquainted with what they do." Letting one's gaze roam unlawfully arouses desire and drives the mind to excessive fantasies.

To avoid this, refrain from unlawful looking and indecent images, avoid places where women are numerous, and increase your fasting.

Know that idleness and solitude excite desire, so occupy yourself with obedience to Allah and what benefits you in your religion and worldly life, and keep company with the righteous. You may also seek assistance from doctors after taking these preventive measures.

The "disease in their hearts" mentioned in Allah's Almighty saying: "In their hearts is a disease" refers to hypocrisy and doubt in religion.