i've read the raws (slowly) since this one's taking forever to scanlate :-(.
in case anyone wants i can summarize in more detail what happened after the last scanlation (62ish), but a short gist of the very end is the boss guy kidnaps rena to save his dad and has an underling derail agawa which causes him to get into a car accident, but luckily asou gets there to save her. rt as she's about to turn small, the doctor girl comes and injects concentrated acs into her which stops the transformation. at the hospital, rena's by agawa's side until he wakes up from his coma. she tells him that the doctor came up with an injectable form of the enzyme, 5 times a day is worth 1 kiss. he says hes happy that she no longer needs to kiss him to survive, but has a bit of a sad expression. later she tells him she wants to be by his side, since he took care of her, and she wants to take care of him, and she's long since loved him so this is what she wants. but he says no, you need to depend on urself, not on others, and that's what it means to be an adult, basically forcing her to become an adult. she leaves for canada to study. at the hospital, asou talks to him, he says that he wants her to grow up to become an adult and not have to depend on them, and that she'll find someone else to love and will forget about him. asao tells him she wants to be with him, and they end up together.
10 years later she comes back. she writes them a letter. she tells them she wrote a book, tells them a bit about her experiences (including how some 20 year old asked her out, but she replied she was 30 years old, and the guy said 'wow japanese girls really do look young!'). she then talks about about her experiences and stuff and how it's made her grow up and stuff but says that she still wants to go back where it was the three of them being together (a motif throughout the latter part of the series was that the 3 of them would continue being with each other). so she says that she wants to return to see if they would accept her now.
the last panels are:
letter: Have I become an adult? Will you two accept me now? To confirm this I must return to Japan.
asou/agawa: You're back! Rena!!
renal: I'm back!
with the implication that it's gonna be the three of them living together going forward.
honestly i have no idea why anyone would think asou married her boss. even if all you can do is just look at the pictures there's nothing that would suggest that. all in all it's a fairly happyish ending, not sure why people keep calling it a bad one, esp compared to the other cupid mangas.