1. They lived together for over a year before the girlfriend became PR making them common-law spouses
2. The girlfriend got PR as a dependent on her parent’s own PR application
3. Because the girlfriend had a common-law spouse, she was no longer a dependent by IRCC standards, therefore, her parent misrepresented
4. IRCC mandates that everyone who applies for PR must include their common-law spouse/married spouse/children in the application, the penalty on not doing so is that those who are undeclared are no longer considered members of the family class, therefore can never be sponsored
In conclusion:
It looks like the girlfriend’s parent chose to misrepresent to be able to get the daughter PR but due to this lie, the boyfriend is no longer a member of the family class. It does not even matter if they get married, he is forever excluded.