All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
We congratulate you on your repentance and determination to adhere to the Islamic rulings in your day-to-day life. In fact, a Muslim should take the matter of his religion very seriously since he will be held accountable in front of Allaah for his every deed.
Allaah welcomes every repentant regardless of his sins and forgives all his sins if he sincerely repents.
Islam does not permit any personal relations between sexes regardless of how pure and innocent they are. Satan is in ambush of human beings, he leads them to bad consequences through mixing. So, we advise you to end all your relations with the girl since it leads to much harm and strengthens Satan against you. For details, please read to Fatwa: 84281.
You should pray Istikhaarah and contact the guardian of this girl and convince him that you are a suitable match for her and he should not delay marrying her to you if possible. To know how to pray Istikhaarah, read to Fatwa: 81434. If you succeed in marrying this girl, then praise be to Allaah, the Glorified and the Exalted; be adherent to His religion. If they do not agree to marry her off to you, then you should search for another religious girl to avoid temptation. Allaah, the Glorified and the Exalted, will facilitate for you a pious girl. No doubt, all the good is in what Allaah, the Glorified and the Exalted, has decreed for you.
Allaah knows best.