This is a story about love and heartbreak. It deals with themes of facing your emotions head-on rather than being insecure and ignoring your feelings. There are many moments of angst and sadness, and we see characters growing over time. And friendships being formed. The tears are so globulous, it's great. The story becomes a tessellation of love triangles. When one love triangle is "resolved," another one forms to take its place. Some of the love triangles are genuine, while some of them are caused by misunderstandings.
There are two ways that the bittersweet aspect of romance is evoked: 1) A character loves somebody, but that love is not reciprocated; and 2) A character loves two people, but feels they must choose one. In fact, it's implied that people can only truly love one person at a time, so one of the loves must be lesser. And it's only after you move on from the previous love that you can truly love somebody else. According to this manga, the greatest determiner of true love is seeing if you're immediately able to spot your lover even in a crowd of people.
I definitely find its portrayal of love as a shuffle where eventually everyone will fall into an ideal pairing to be idealistic and fantastical, but that's not a bad thing. Being over-the-top is what makes these stories more fascinating than the mundanity of realistic romance. But as a warning for people who might get a false expectation for real-life romance from these stories: Just like we wouldn't expect the life of an actual pirate to be like Luffy's, we shouldn't expect real-life romances to be like this.