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.
Dear brother, do not forget that this life is very short and soon you will leave this world and you will be held accountable for all your deeds.
Any personal relation with any marriageable women angers Allaah and incurs His wrath. So, you have to cut all such relations immediately, ask Allaah to help you forget this girl, and you should thank Allaah that He has granted you a wife; the lawful way to satisfy yourself.
For details in this matter read our Fataawa 81356, 87705, 84544 and 87553.
We ask Allaah to protect you from evil and form that girl.
Allaah Knows best.