Are sexual practices between a young man and a young woman (without penetration) considered zina and a major sin, especially if they continued for years and ended with the young man abandoning her, and will the girl's repentance be accepted after her remorse and fear of God's punishment?

Unlawful foreplay without penetration is not considered Zina (fornication/adultery) that necessitates the prescribed punishment (Hadd). No matter how great a sin, sincere repentance is accepted and erases what came before it. Allah accepts the repentance of His servants and pardons sins. Repentance involves abandoning the sin, regretting it, and resolving not to return to it, along with concealing one's own past transgression. He who repents from a sin is like one who has no sin, and Allah rejoices at the repentance of His servant and replaces his evil deeds with good ones.