We don't know if Naina is staying with Suraj or just in the same city. I think they aren't a couple because if they're together Imli wouldn't be so sure they won't have kids.
I don't think they'll show them as a couple because then Suraj will have a duty towards her and this will make her equal to Chakor.
If Naina is staying in the same city, there is nothing Suraj can do to make her leave.