What Should be My Next Nikon Lens?

Hi there! Im abran, My uncle got me into Photography a year back, when I was a freshman in High School, And since then, I kept liking it. I First Used a Canon 600D with 18-55 kit lens, and Currently Im using. A nikon d7100 with 18-140 VR lens. I bought this camera a few months back, Im still learning though. I have saved up around $500 for a new lens ( It dosent have to be $500 exactly ) I mean I cant spend more than 500 on a lens. I like to shoot Landscape more, rather than portraits. Few of my friends suggested me to get the Nikon 35mm/50mm prime lens, But im not sure if it will be a good idea, because Mostly primes are for portraits. I do capture portraits too, but not always. Someone who has experience in Photography would be a little helpful to decide what kind of lens I should Get.

This is my album in my Facebook: https://www.facebook.com/abran.tasrif/albums/639887112690124/

To show what type of pictures I take.
*Please dont judge my photos, Im just a beginner*

Thank you for your attention:)

Read more: What Should be My Next Nikon Lens?