This sad (yet undeniably hot) chapter is actually quite realistic. In a world where at least ninety percent of men are poor fucks, when a woman finds a guy with a big cock who knows how to use it, she's often willing to share him (reluctantly) with other girls. After all, if she dumps him out of jealousy, that means she gets no more sweet lovin', while the other girls have all the fun. For a woman, that's simply unacceptable.
Ikkun is a cynical cad who understands all that perfectly, and he takes full advantage of it. He practically rapes Erina, but he knows she's unlikely to resist because she's highly aroused, envious of Riko, and eager to find out what it feels like to be fucked into an ecstatic stupor with a big, fat cock.
At the end, Erina realizes that, like Riko, she's now hopelessly enthralled with Ikkun and his "good points," and she knows that, from then on, she'll hungrily fuck him whenever he whistles for her. She'll be thinking of him when she fucks her boyfriend, wishing Ikkun's big, fat, burly cock was inside her, instead. Ah, love.
We have seen variations on this theme in other chapters. For example, in TANABE's "Koorimachi" series, Naeshiro is a cheerful horndog who's much more likeable than Ikkun. He has a stable of girls, but his favorite (rather surprisingly) seems to be Koorimachi, a plain, nerdy glasses-girl who never had a boyfriend (so there's no cheating angle).
The chief difference between Koormimachi and Erina is that Koorimachi isn't infatuated with Naeshiro (in fact, she doesn't seem to feel any sort of affection for him at all). She simply decided it was time to give up her virginity, but she wanted GOOD sex, so she allowed Naeshiro to initiate a sexual relationship with her because he was a proven stud who could give a girl a good time. Performance over romance.
Well, in a Higenamuchi release you can already tell what's going to happen the moment he mentioned her already having a boyfriend.
Hmm, considering that ending though...So if she continues this cheating relationship with him, then in a way, what her friend said is basically giving her the all green sign, right?
I never considered that as an explanation to the last page, which sounds rational. I just thought she was putting on a judgmental façade toward Ikkun as a continuation of her balderdash about how much she didn't like him. Yours makes more sense.
Riko isn't giving a thought to anything Ikkun and Erina might've done, or might do in the future. The significance of the last page is that Erina realizes that, just like Riko, she's now hopelessly enthralled with Ikkun and his "good points," and she'll go on cheating simply for a great fuck.
Your take makes sense too, btw and I agree that Erina wants it both ways. Well, I don't know what was rolling around in the writer's mind so my conjecture is going to be creative at best and, unfortunately, I have no desire to read thru this story again so I hope I remember enough to respond knowledgeably. I don't remember Erina being aware of Ikkun being a sexual tyrannosaurus at the very beginning, but I do remember her thinking some disingenuous stuff about him while the three were hanging out. Stuff like, "He's too overconfident...". Not being cocky (lol), brash, rude, braggadocios, narcissistic but overconfident. Being "too overconfident" sounds like there's too much of a good thing, which in this case, I don't think exists. So I think this is another tale of the unfaithful and immoral chick trying her darnedest to convince herself to deny her overall attraction (not just he might provide a pornstar level lay) to some dude, only to succumb to her own temptation. But yeah, she probably realizes the overall quality of a relationship with somebody like Ikkun has a low ceiling so she wants to keep the sensible option off to the side.
For gammenon: Erina wants it both ways. She's hot for Ikkun's big, fat cock, but she has no interest in him as a boyfriend, so she's unwilling to give up her current boyfriend because he is her "official" social companion---the one who squires her around in public.
And as for Erina, that's ok - just end it with the boyfriend and be honest about it. She's in it for the dick, nuttin' wrong with that. I just really hope the boyfriend would understand that if she wants to be part of Ikkun's waiting list harem, let her [go] and find somebody else. It would be satisfying if one of these type of stories had a scenario where it blows up in everybody's face.
Aside from me still having integrity, that Erina chick kinda reminded of when I tried to stay on a diet a while back. My brother during that time gave me a scrumptious marble pound cake and I was dumb enough to think eat I could eat it in moderation. I tried a little self denial strategy telling myself how bad the cake was for me and it really didn't look that good. I ended up eating the whole thing in less than a couple hours. It tasted as good as it looked, tho'.
As for the story, I liked how Erina stayed full-blown hypocrite to the very end. Hentai wouldn't quite be hentai without sluts like her.