夫 is “husband”, 妻 is “wife”, together they mean both “husband and wife” and “married couple”. It is extremely common in Chinese to form compound words by juxtaposing or opposing two characters to refer to a broader concept encompassing the individual characters. To quote a few examples, 父母 (father+mother) refers to “parents”, 大小 (big+small) means “size”, 荣辱 (honour+disgrace) is “reputation”, the list goes on and on.

Having “husband+wife” as “married couple” and “father+mother” as “parents” is of course heteronormative but it’s also a reflection of what society was and still is to this day. New words were coined to refer to same-sex couples such as 夫夫 (fufu, husband+husband) but that’s modern terminology. It might be worthwhile to bring up the fact that 夫夫 is used multiple times by MXTX to refer to Wei Wuxian and Lan Wangji outside of the novel itself. It’s on the webnovel frontpage as well as several chapter blurbs:

夫夫双双把山下 “The pair of husbands leave the mountain” (chapter blurb 20)

夫夫齐斩辣鸡洋，星岚箐尘埃落定。义城篇，完。”The husbands chop up trash [Xue] Yang, aftermath of [Xiao] Xing[chen], [Song] Lan and [A-]Qing, end of the Yi City arc”, there’s a pun in there as “trash” (垃圾 lājī) is written as the homophonous “spicy chicken” (辣鸡 làjī) (chapter blurb 42)

夫夫吃糖日常, ”Husbands eating sweets everyday”, eating sweets is internet slang for public displays of affection. (chapter blurb 116)

These are all written in a humorous and light-hearted way as you can see. This kind of tongue-in-cheek author notes don’t make it in physical copies when novels get published but they’re representative of the very casual tone full of slang allusions on webnovel platforms where novel recaps sort of sound like shitposts. With that said, I would be remiss not to mention that the blurb of chapter 7 is 霸道含光君的疯癫小逃妻？？？, “The overbearing Hanguang-Jun’s crazy runaway wife???”. This sounds terribly awkward but it’s referencing stereotypical characters in het romances such as the pushy CEO and the young woman who is wary at first but then fall madly in love with him. You know the type. There are plenty of those in novels written by Western authors as well.

While Chinese is not outwardly a particularly gendered language (no grammatical gender with distinct masculine and feminine forms as it is common in many Indo-European languages and other language families), it is a language in which social roles and positions are heavily codified as seen through the use of honorifics and this social divide intersects with male/female differentiation. For instance, there is a number of characters that can be used to signify “to marry”, like the gender-specific 娶 or 嫁 depending on whether the subject is a man or woman, the first character is composed of “取 take+ 女 woman” and the second of “女 woman + 家 home/family”. As I mentioned here, marriage was not equal in ancient times as the bride was leaving her family and entering her husband’s household. At the end of the novel, Wei Wuxian effectively marries into the Gusu Lan Sect, thus holding the social position that would traditionally be the wife’s part. What is interesting however is that the story and the main characters deconstruct typical gender roles. As I was saying, the Chinese language itself might not ostensibly gendered but Chinese traditional society certainly was. There’s a saying that goes 男耕女织, “Men plough and women weave” to describe pastoral life. That should remind you of Wei Wuxian’s dream (ch.67, 117), he has no qualms imaging himself as the one working the fields and doing outdoor labour while Lan Wangji stays in their little cottage and does the housekeeping.