How can the desire to marry a girl who is committed to prayer and fasting but does not wear a hijab be reconciled with the condition of wearing the hijab, knowing that transgressions short of actual zina have occurred?

What happens in terms of acquaintanceships and love relationships between young men and women is a gateway to evil and corruption. One must hasten to repent to Allah by severing the relationship and closing the door to temptation. You are not obligated to marry her because of what happened, and you should not marry a girl who insists on displaying her adornment (tabarruj). Rather, seek a righteous girl who will help you in matters of your religion.