Well...she was dating Paris Latsis but I am pretty sure they broke up because he had to go back to the Navy in Greece. I think, I am not positive though...but Nikki did a Q&A and mentioned how she got her сердце broken. Here's the link:
link and she starts talking about it at like 1:35 but Ты can go back further to hear all of it...but she
might have been talking about him.
But I hope Nikki and Kellan get together!!!