It's a legally distinct parody of an actual matchmaking/dating app called happymail, you can download it from your phone's app store (the real app, not the parody) assuming you're in the region. There
are cases of people using the real-life app for compensated dating purposes, I should know, a former co-worker of mine used it for mama-katsu on top of our then part-time job.
If my theory about her voluntarily disappearing to protect Naoto from herself is correct, and adding to Luna's seeming insistence to being Naoto's "Big Sis", as
normal society dictates. Her dependency on Naoto renders her unable to stay in a stable relationship with other men, with them somehow reminding her of her father who went out to get milk, and she eventually falls back to Naoto every single time, with the frequency of her
trying and failing to keep a single guy ending up being the catalyst to the rumours about her.
One could argue that Naoto effectively NTRs all her prospective boyfriends/lovers simply by existing.
I reckon Luna is feeling the pressure of
Alabama Naoto's advance closing in on her, and her move now is an effort for her to keep being Naoto's "Big Sis".
Hiba appearing would be great as a support for the next chapter, as she likely
would know what the readers and Naoto wants know about Luna's personal relationships.
Thanks to getting dragged into a few goukon by the former co-worker that I mentioned earlier, I can say from observation and experience that I can both confirm AND deny this statement.
Not every encounter ends with a "happy ending". It's a coin toss most of the time really, and it relies completely on the other party. How open they are, how desperate they are (more likely with runaway teens with no income, less likely with actual working adults), and how much you're willing to pay up are all factors in determining which ending you're going to get.
More often than not, you're just getting a new drinking buddy.