It's not clear what kind of "romantic novels" the subjects of these studies had read. However, it is clear from the description of the story used in the study, that it did have a central romantic relationship ending with the characters living "together happily."
From the "Highlights":
Romantic jealousy has a negative mediation effect between identification and parasocial relationship in existing players.
Avatar images promote game experience for players unfamiliar with romantic stories
Avtar images lead to jealousy and undermine parasocial relationship for players familiar with romantic stories.
In study 1, potential players who liked/disliked reading romantic novels but seldom played RVGs were asked to play a brand-new romantic game with or without the female avatar's images, and then they filled out scales on avatar identification, parasocial relationship, and romantic jealousy. [...]
A story script from a popular RVG Mr. Love: Queen's Choice was adapted. This game has more than 4 million daily active users and a monthly turnover of almost 300 million CNY at its peak. In the plot, the female protagonist accidentally meets the male protagonist, then they interact in the company and daily life, fall in love, and eventually live together happily. Two versions were created with or without the female avatar's images [...]
for those potential players who had never played RVGs, whether they liked reading romantic novels or not, or whether they were briefly experiencing the RVG with or without avatar images did not significantly affect players' avatar identification, romantic jealousy, and long-term PSR [...]
To summarize the effects of avatar images, the results of Study 1 highlight their function in assisting with instant PSR when players encounter this type of game for the first time. However, it had a slightly negative effect on those who liked romantic novels, as they might already be equipped with the ability of mental imagery, so images hindered them from immersing in the story.