All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
We pray to Allah to protect you and us from all evil and make us firm and steadfast on the right path. We advise you to immediately leave this girl who is inviting you to commit forbidden acts, and you should keep away from her and all other non-Mahram women. In fact, it is forbidden in Islam to establish an affectionate relationship with non-Mahram women as this is against the commands of Allah, which urge the Muslims to lower their gaze and prohibit them from being alone with non-Mahram woman. We do not advise you to marry her unless she sincerely repents, becomes pious and adheres to the right path. Otherwise, it is very possible that she may be unfaithful to you and she may give birth to children who are not from you.
Hence, you should admonish her, frighten her with the punishment of Allah, and explain to her that this is a shameful act. Moreover, you should explain to her that by doing such an act, she is not only disobeying her Lord, but also dishonoring and humiliating herself. This should be done only if she is a Muslim. But if she is a non-Muslim, then you should stay away from her as she will spoil your religion and you would have combined two sins: illicit relationship and socializing with a non-Muslim; both are evil.
Therefore, you should hasten to marry in order to protect yourself from forbidden acts and you should stop all kinds of illicit relationships. The Prophet said: “O young people, whoever is able to marry should marry, and whoever is not able to do so, he should fast, as fasting diminishes his sexual desires.” [Al-Bukhari and Muslim]
Allah knows best.