A great spin on the nostalgic summer romance! I got the sad endings first, and I think they're even more fitting than the happy ending (or maybe I'm just prone to melancholy). But there's something compelling about Kai staring out at the ocean, thinking about everything they've lost forever. Bittersweet and wonderful.
[Spoilers]
Even more tragic if you think about how, by giving up on their dreams, Kai unknowingly locks themself out of ever seeing Caspian again. They lose so much by giving into the drudgery of daily life, and don't even know it.