Okay from what I'm seen from the promo pictures of today's episode. Sean is already close to Nay while in SIMM they didn't interact (as I remember).
So yeah they are doing that because of WinnySatang recent celebrity (and I'm happy to see them together again ngl) and it was predictable from GMM. But I was hoping to see Nay and Sean getting close slowly, with an open ending instead of what we are gonna get.
So my theory :
They are going to tell us that Nay and Sean go close (even got together) secretly off-camera. And that they had a fight but since their closeness is secret Sean couldn't complained last episode.
I'm pretty sure Sean didn't want to go to Chiang Mai because he knew Nay was there and since they are fighting... because his reason for not going to Chiang Mai was so suspect. (Come on in a show a character who only say "I can't, I have something to do" without explanation is always foreshadowing)
If we didn't know that Nay was the only one saying yes to the trip I would have say that Sean had a date with Nay, but it's not the case Nay was going to be in Chiang Mai anyway.
In the last promo pictures Nay and Sean are sitting next to each other, soooo close. So I think it confirms my theory.
Anyway, I hope I'm wrong because this would feel even more forced to put two characters together off-cam when they never interact before. (I know some of you didn't want them together in any case but I think it could have been okay if we had their development)