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.
There is no doubt that this action is strictly forbidden under the Sharee‘ah (Islamic law) and is regarded as immorality. One has to sincerely repent to Allaah The Almighty, intensify seeking forgiveness and regret that action.
Nevertheless, this does not affect the permissibility of marrying that woman. Even if this action is prohibited, it does not prohibit marriage.
Allaah Knows best.