Romance is in the heart(s) of the beholder(s).
As for semi-quiet, if you don't mind a primitive (not drinking water, no indoor plumbing) campsite, I highly recommend
Hill Country State Natural Area in Bandera, TX. There are campsites that are a short (few hundred yards) walk from your car, or multi-mile (about 2-3 mile) hike-in campsites -- I've camped in the former and had peaceful, relaxing multi-night camping but the primitive sites are even nicer -- I always make it a point to hike by them during hiking and mountain biking trips, and often they're all available.
Anywhere can be romantic, though. Some of our fondest memories are of funny things that happened when we were in less than optimal campsites... like our Enchanted Rock SNA campout on a Wednesday and Thursday night (we thought those would be the best days to avoid crowds during the school year). Instead, several school buses from a Texas school district descended upon the park and stayed both nights, including the first night when two huge camps of teenagers from the group sang "99 bottles of beer on the wall" all the way from 99 to 1... anytime we're surprised by something now, it's not uncommon for one of us to mutter, "I can't believe they sang it ALL THE WAY THROUGH!"

Sure, we didn't sleep well that night and it was highly annoying, but memories are romantic too -- shared history and experiences -- even when they're nothing more than a temporary annoyance shared with someone you care about.
18 years together, and counting (incl. 8 years as husband & wife)