If they are not a couple they have been and very much in love with each other. People can sometimes find medium ground to evolve and continue to be in each other's lives even if they stop being a romantic couple. Somehow those people may no longer be a couple but they will not be with anyone else either and that's how they survive together. Boun has this strong look in his eyes of love when he is looking at Prem. Prem's heart will always belong to Boun. Prem said in public that if he could he would give his heart to Boun because Boun was born with a weak heart. That made Boun cry right in front of everybody.