What does this horizontal line mean and will it go away? (Photos)

It is too early to say what the line is.  It may also disappear as the swelling settles over the next few weeks and months.  The line probably corresponds to the edges of the nasal bones and bones of the face that we call the pyriform aperture. I advise you take the photos to your surgeon and discuss your concerns.  Be aware too that photos can make a problem look worse than it is.

Hi and welcome to our forum!
The performance of rhinoplasty involves the separation of the
nasal bones and cartilages from overlying and underlying structures,
fracturing the nasal bones, removing excess bone / cartilage, reshaping of
the remaining bone and cartilage. The significant intraoperative
trauma causes swelling (which may be asymmetric), which will make your
nose look large and wide and most likely accounts for the horizontal line. This will improve markedly over the first 8 weeks,
but will take at least a year for your nose to assume its final shape and
size. It is far too early to assess your final appearance. 
Continue followup with your plastic surgeon and discuss your concerns.
Best wishes...