Oh boy! OP - I read the knot discussion and I agree with PP, you aren't going to get the answers you're looking for here.
Listen, I'm so sorry that you have been in abusive relationships in the past. But don't let that delude you into thinking that this guy is the guy for the long haul. At 18 and only knowing this guy 5-6 months, you're just wrong. I hate to say it, but it's true. Marriage is a forever commitment. The first couple months/year of a relationship is the puppy-dog phase, you're infatuated, can't stand to be apart, etc. But that wears off quick. I doubt you want to be 18/19 years old with 4 past partners who were abusive AND and ex-husband.
I would really love to know your parents line of thinking in all this. I would also like to know how old this guy is because that was never addressed over on the knot as far as I can tell. Chances are, you parents are right. Maybe it's not the guy that's their issue... perhaps it's simply the momentum of the relationship.
I'd really take the time to slow down, enjoy being BF/GF, assess the relationship as you go, ENROLL BACK IN SCHOOL and re-address the topic of marriage in a good 5 years or so. That's the mature and adult thing to do. Rushing into something you are so clearly not prepared for is infantile; vying to achieve adulthood through marriage does not make you more mature, it's actually a demonstration of a complete lack of responsibility.
If my memory is correct, you scheduled the wedding for a few years from now? If so, fingers crossed you come to your senses at some point. Really, I'm sorry, I don't want to be a jerk but if you go ahead and get married any time soon (and heaven forbid you have a baby) this does not end well for you.