All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Stories are imaginary or real accounts of some happenings that took place in the past, are occurring now, or will/might take place in the future. The Sharee’ah rulings regarding stories differ according to their content, form and objective. For instance, a story that depicts some real events that took place between a wife and her husband which aims at a noble objective and whose content and form are free from anything that could have a bad influence on the listener or the reader takes the ruling of telling a true unbiased or uncorrupted information which is what is lawful, even if there is throughout that story a description of sentimental feelings between couples, provided there is no description of sexual intercourse. The evidence for the lawfulness of such a story is what is narrated in the Hadeeth books about what happened between the Prophet and his wives. ‘Aa’ishah said: “The Prophet used to drink (from the vessel) putting his mouth exactly on the place where I (had put mine) drinking from what I had left over while I was menstruating.” [An-Nasaa'i]
‘Aa’ishah also said: “I would drink while I was menstruating, then I would hand it (the vessel) to the Prophet and he would put his mouth where mine had been and drink, and I would eat flesh from a bone while I was menstruating, then hand it over to the Prophet () and he would put his mouth where mine had been.” [Muslim]
Muslim also reported that ‘Aa’ishah said: “The Prophet used to put his head in my lap while I was menstruating and read the Quran.”
Besides, Um Salamah mentioned that “She used to make Ghusl along with the Prophet from the same receptacle.” She also narrated that “He used to kiss her while fasting.” So, these events and many more took place in the home of the Prophet and the biographers and narrators reported them for a noble purpose.
This is evidence that similar stories are lawful if they are for a similar purpose and if they meet the aforementioned restrictions regardless of whether the events were real or imaginary as long as the aim behind them is a good one.
As for the stories that describe unlawful relations between men and non-Mahram (marriageable) women; which instead of warning against such deeds, elicit them and beautify them by using attractive and tempting words and expressions, then there is no doubt that such stories are unlawful.
Allah Says (what means):
• {… not unlawful sexual intercourse or taking [secret] lovers.} [Quran 5:5]
• {… neither [of] those who commit unlawful intercourse randomly nor those who take [secret] lovers.} [Quran 4:25]
Moreover, Muslim reported that the Prophet said: “Beware of entering in a place where there are women.” In another Hadeeth, the Prophet said: “None of you (men) should stay in seclusion with a non-Mahram woman as Satan is their third.”
The story that you mentioned in the question is unlawful because it depicts some intimate relations, beautifying them to the listener or reader. The unlawfulness becomes more emphatic when there is a description of Zina (fornication or adultery) and its introductions, such as kissing, touching …etc. Such stories fit what Allah describes in this verse. Allah Says (what means): {Indeed, those who like that immorality should be spread [or publicized] among those who have believed will have a painful punishment in this world and the Hereafter.} [Quran 24:19]
So, reading such stories excites the libido and the sexual desire, driving the person to sinful thoughts and love. Any story that causes the above is forbidden because means take the ruling of their ends. So any means that lead to a sin is a sin in itself.
Allah knows best.