Is a young man considered to be committing a sin or to be ill due to being aroused when reading or listening to any content related to sexual culture, even if it is religious or medical, or when discussing these topics in general with his fiancée?

Thank you for your zeal for your religion. The arousal of your desire upon hearing or reading sexual matters is natural for your age and no cause for concern; it will subside after marriage. The cause might be an increase in hormones, and you can consult a doctor if the condition persists after marriage. We advise you to hasten to marry and continue fasting beforehand, and to avoid anything that arouses your desire, such as speaking with your fiancée or others, for your fiancée is a non-mahram (definition) before the marriage contract.