Girlfriend's parents threatened to hold her college fund and kick her out of the house when she turns 18 if she continues things with me.

I don't want to go into many details, but we're both 17, turning 18 in about 4 months, and things have never been great with her parents. We aren't official, at least obviously not with her parents' blessing, but have been trying to make it real for a year and a half. At first, they said they wanted her to focus on school, then that I needed to prove myself, and now that we aren't good for each other. I'm Catholic, and she's protestant but doesn't think it has anything to do with their decisions; they don't even know me. Her mom is the assistant principal at our school, but besides that,t we haven't had any interactions outside of a school setting. Ive tried to do something so they can get a read on me and even tried talking to her mom, but she avoided me. Essentially, they didn't want us talking much, and we met up a few times to talk, and never did anything more than kiss, but they found out and weren't thrilled. I really like this girl, we've talked alot and I know her better than anyone else by a longshot but i dont know if it's best to cut things now. Would it be selfish to try to find a way to continue? Should I cut it for both of us?