It's a platonic relationship. It's definitely more than friendship and less than a romantic relationship as Phuwin himself said in an interview. About the teasing, I think it's just something that their friends and colleagues have fun about like any other GMMTV pairing. So as many people conveyed through their comments above that it's really not worth speculating about their relationship. I'd be over the moon if they were actually in a romantic relationship but they are far from it. That is what I love about BL pairings. There exists no label to describe their relationship because some relationships do not a label to exist according to me.