Should I leave my girlfriend with whom I almost committed zina, and who did not stop me, knowing that we agreed to marry after university?

You must awaken from your heedlessness, for what you did with this girl is forbidden. Repent to Allah with sincere repentance, because you are defying Allah with your sins. If the girl repents with sincere repentance and her waiting period (iddah) ends, then there is no harm in you marrying her. This is based on the saying of Imam Ibn Qudamah: "If a woman commits fornication, it is not permissible for one who knows this to marry her except under two conditions: The first: the expiry of her waiting period (iddah). The second: that she repents from fornication." And the saying of the Prophet, peace be upon him: "The one who repents from sin is like one who has no sin."