Guess the bottom: What is Sanqiu that I haven't seen for a day?

This sentence comes from picking songs in the Book of Songs.

I haven't seen you for a day, like March!

He chooses Xiao Xi, but he doesn't see you for a day, like Sanqiu Xi!

I haven't seen you all day, as if I were only three years old!

One said that her husband missed his wife who went out to work, and the other said that a man and a woman often went to the mountains to collect medicine together, which hit it off very well. After not seeing each other for one day, three months, three seasons and three years, they will feel as if they will miss each other. And amethyst green scorpions, lingering in my mind, even if I don't go, Zi Ning won't listen ... A day is gone, just like March! This reminds me of a joke told by a physics teacher. Einstein explained the theory of relativity to people: "In hot summer, it takes several years to sit in front of the stove, but if you sit next to a beautiful woman, it only takes a few seconds." It seems that thousands of years ago, the ancients in China understood the essence of relativity when they were in love! So later generations have a visible day. For example, the idiom Sanqiu (or a day in Sanqiu) can be used to describe the lingering between lovers and husband and wife, and it can also be used to describe the caring and inseparable relationship between like-minded friends. The literal meaning is easy to understand, but it is not so easy and easy to really understand.