An asmachta is used by chazal to attribute to a pasuk something that is not in the pshat or deoraysoh-level drash. It means that the Torah is hinting out to something beyond what it is directly talking about. Here, the rishonim who discuss the mitzvah of veahavta and its laws do not mention the gemara in kidushin lf asur lekadesh… ad sheyirena.
Chazal are talking about a halacha that seems to be mederabonon in nature(i will imyh look that up because I’m not sure of it at this time), but even if one is violating veahavta medoraysoh by disliking another jew, there’s no reason to think that it is specifically talking about one’s wife more than any other jew, so applying veahavta is not pshat or drash – it’s a very clear example of asmachta, since like you and I quoted, the word reah/reus is used in regards to marriage.