Yeah, the reeds are I Ching

I think (?) Baidu is saying that the theme is that women who fall in love stay in love, while men easily fall out of love. General agreement is that the three years is literal, but one source says that it just means that after a few years, the marriage gradually breaks down.

The carriage curtains getting wet is just that she is now returning to her natal home (and crossing the Qi river again)