Why don't your parents know he's a soon-to-be college graduate? An already present lack of communication won't help your cause here.
Otherwise, remember that our culture is shifting. Time was, it was an accomplishment to graduate high school — forget college. And a dependable, thirty-year job could be obtained based solely on that.
In today's world, it is natural for your folks to worry about your future financial security. Start by reminding them you're happy with this fella. But also remind them that, in today's world, a degree doesn't guarantee work anyways.