, that had been my main gripe too, at the beginning of the Lakorn (meaning: ep 1-4, before the great reveal) Why the hell would "nice guy" Ramet be so in love with Pim even when she was being so bratty. I tried to rationalize it, and it came down to the following:
1) she was so stunningly beautiful - of course this is the most "obvious" reason since Paa'Jaew drew the "love at first sight" card again.
2) her dad was Ramet's idol and he did say that his daughter is his inspiration so Ramet figured there must be something more about her that meets the eye.
3) "Perfect" guys like "perfect girls" - i.e. high maintenance. Being a manager of a hotel means he has to be on top of everything. The fact that he was able to snag a prima donna is a feather in his cap, even though he'd have to teach her a thing or two about niceness.
4) gut feel that she is nice - Ramet had this whole speech about him thinking with his heart and following his gut feel more than logic. (I think it was a dialogue with Nong) Of course that had been a self serving statement and through the course of the Lakorn he had been more logical than impulsive (maybe also because he is "once burned, twice shy" with Pim so even when he said he wanted to believe her just because he believed her in that soup incident with Matavi, he still chose to be a logical jerk about it and made her apologize). But he also had that speech about the hydrangea so maybe he knew (or at the very least, he wished) Pim's coldness was just a cover and really she is a sensitive, kind soul.
5) ok this is farfetched but look at his sister and look at Pim. It's not incest, but you know how some guys compare their ideal girl to their sisters? Pim fits the mold of the perfect, hi-so woman who is so poised and elegant like Ramet's older sister (and remember he has 2 older sisters, meaning he is not only the youngest, but also an only boy)
6) he hadn't really seen her nasty side first hand - Pim was trying to snag him after all so maybe Ramet took that positive signals and kind of blurred out the negative signs.
Still, those reasons still didn't make it justifiable for Ramet to like Pim from ep 1-4. I really couldn't understand why Ramet who is supposedly smart is actually an idiot (for liking someone on a superficial basis). He is actually the opposite of James's previous P'eks (Puttipat, Ittirit, Saran and Neung, especially Neung) who initially thought of the n'ek negatively, had prejudice against the n'ek from the beginning he only softened up and gave in to love completely when he got to know the n'ek better. Ramet didn't know the n'ek much but already put her in a pedestal from the love at first sight scene, only for him to crash and burn when he realizes she duped him. In keeping with the Swan theme, maybe it's an allusion to Swan Lake, where the prince also got duped by the villain with a princess decoy *sweatdrop*
So towards the end when he gets asked who he loved more, old Pim or new Pim, he answers both, it seems to be like he fell in love with her anew when she shed her bratty side. And whatever he felt for her before the betreyal scene just seemed to have been put aside because by ep 12, he was truly madly deeply in love when Pim likewise became more well-rounded so to speak.