"伊人" refers to the person you like in your heart. The meaning of this sentence is that the lover whom I long for day and night is standing on the other side of the river. Combining with the first sentence, we can see that this is the author's helplessness and sadness when facing his sweetheart, who he longs for but can't.
"The so-called lover is on the other side of the water." The sweetheart you love is on the other side of the water. The jianjia is green and the dew is like frost. The beauty is on that side across the autumn water. Love is infinite, imagination is like seeing. Romantic sadness, giving people unlimited room for reverie. Often the person you love the most is on the other side of the water. It seems to be close at hand, but out of reach. I can only look at her from a distance. I can see her glance and smile, but I am in two different worlds with her. Water, a clear and pure place, a dreamlike place.
The sea is also water, an insurmountable distance that is infinite, vast and thousands of miles away... The person you love most is on the other side of the water...