Are the girl's parents entitled to complain to the ruler years after she has been living with me without anything happening? And what would be the ruling?

After repentance, one must turn away from the whispers that remind of the sin, and suffice with renewing repentance, seeking forgiveness, and praising Allah for guidance. The sleeping of a non-mahram woman with a non-mahram man does not necessitate a Sharia prescribed punishment (hadd), but the ruler may discipline the perpetrator with an appropriate punishment. Proving the occurrence of such an event, especially after a long time has passed, is very difficult.