What must a young man who committed fornication during daylight hours in Ramadan do after repenting, and what is the ruling on his fasting and how should he make it up?

Sexual intercourse during the day in Ramadan is one of the gravest nullifiers of the fast. Whoever commits it incurs sin, must abstain from food and drink for the rest of the day (imsak), and is obligated to make up for the fast (qada') and offer a severe expiation (kaffara mughalladha). The proof for this is the hadith narrated by Abu Hurayrah (may Allah be pleased with him) that a man had intercourse with his wife during Ramadan, and the Prophet (peace be upon him) commanded him to free a slave. If he could not find one, then to fast for two consecutive months. If he was unable to do that, then to feed sixty poor people. As for one who commits zina (fornication/adultery) during the day in Ramadan, he has violated two sacred things: the sanctity of the month and the sanctity of illicit sexual relations. He must make a great repentance, make up for the fast, offer the severe expiation, and strive to get married or fast to protect his chastity.