Are the aforementioned actions—the exchange of kisses and embraces between a young man and a young woman before marriage, without reaching the point of zina (fornication/adultery) or full intercourse—considered zina? And will the repentance of this young man be accepted after his intense regret over these actions, and what should he do?

Ibn Abbas heard the Prophet, peace and blessings be upon him, say: "No man should be alone with a woman unless she is accompanied by a محرم (a close male relative)."

What your friend did—being alone with a foreign woman, exchanging kisses, and embracing—is impermissible and a violation of the boundaries set by Allah. An engaged woman is considered a foreign woman until the valid Islamic marriage contract is concluded. These actions do not constitute zina (fornication/adultery) that necessitates a legal punishment (حد), but they are a sin that requires repentance. Your friend should hasten to repent and seek a righteous wife.