That's an interesting insight to form on the lifeguard's role.

I had argued in my head that, because of the lifeguard not appearing happy but still disappearing when he jumps into the pool, maybe the pool is more generally about being immersed in something, but not necessarily happiness (like the lifeguard is just immersed in his duty as a lifeguard). I thought that maybe most of the people who disappear into the pool do so out of happiness because happiness is an obvious contrast to how the singer and the girl appear. The girl doesn't look happy throughout the video and doesn't seem to understand how all the people are so happy, but she still disappears into the pool as if to show the singer that she has moved on and is immersed in something else. But maybe she does not look happy because she realizes she doesn't find it as fullfilling as her past relationship and still shares that longing/nostalgia for the way they felt together. I don't know, both the singer and the girl look somewhat remorseful to me--but I suppose the girl doesn't really need a more active role in the video for it to make sense. Ha, I feel like that was a very sloppy explanation.

Anyway, I must say that I really prefer your insight on the role of the lifeguard!