Umm, I'd say to live your life well, do your best to graduate with the BEST marks in the world, work hard so your parents can see you are growing up and can make good decisions for yourself.
If you are still together after you graduate, and everyone can see your DF has been working hard towards his career and you are happy together......well as a parent I couldn't argue with that. Hopefully they won't still be sucked in by the family member that caused trouble, and they will see thats in the past/or untrue, and you can start reading bridal magazines with your mum...

good luck!