Historical Context in The River Merchant's Wife: A Letter
Notice the speaker's shyness when she interacts with her new husband. Given that they were friends before this, it's a little strange that she's uncomfortable. Perhaps, as was often the case in 8th Century China, this marriage was arranged for her by her parents, and though she loved her friend dearly, she wasn't prepared for this change in the nature of their relationship.
In 8th Century China, when this poem was written, girls married in their teens, shortly after they reached child-bearing age. This practice, common even in the early 20th Century, resulted in many forced or arranged marriages between two people unprepared for the maturity of their situation. Luckily for the speaker, she knows and likes her husband, but this doesn't mitigate her youth or inexperience.
Here it's important to note that Pound didn't write "The River Merchant's Wife" but rather translated it from the original Chinese, written by Li Po. Li Po's natural images and Eastern sensibility would've appealed to Pound as one of the founding members of Imagism, a movement in poetry dedicated to clarity, rhythm, and precision in diction. Pound's translation is one of the most faithful and well-known, with the only major change being the title, originally written as "Chang'an Memories."