So, correct me if i am wrong, you're inplying that when they both cheating with someone else, he never do vaginal penetration, and she never been penetrated?
I think she actually got railed for real and isn't a virgin anymore.Yes, that's right. They couldn't do vaginal penetration because that would activate the curse. Details are foggy now, but I clearly remember that.
1. Zepar's contract forbids only Satou to have penetrative vaginal sex because doing that with the person he loves most will kill him. That never applied to other men.
2. Rikka only did that because she thought she was dreaming (in reality she was "sleepwalking" or another personality (slut Rikka) took over her body during the "dreams". During those dreams there's no reason not to let them stretch her out because to her "it isn't real". In fact I think the one who ended up taking her virginity was MC's best friend (spicy).
2.1. In fact the only reason she collapsed from shock was because she ended up realizing that her dreams actually happened "in the real world". I personally don't think it would've been such a big deal if they didn't penetrate because then she'd still "be clean" for Satou.
You tight, chapter 48 she said that she wont go all the way with MC or other guys cause it would activate the curse and wouldn't be as fun. Someone else also commented that the raw make this more clear.
3. When she says she won't go all the way with anyone else in ch 48, she's saying that (possibly) to coax Satou into staying with her but accepting that she'd be intimate with other men the way he did with her friend and their teacher.
She still won't have penetrative sex with Satou because that will activate the curse. Again, doing that with other men will be ok per the terms of the contract.
4. When they do have sex before the reset, she says it hurts a bit. I think she felt pain because it's the first time that she got penetrated while she was lucid.
...or because Satou is actually packing and he's the biggest she's had thus far.
5. After the reset, everything went back to normal so it's all a-ok.
I personally think it would've been OK to not do the reset since they both are guilty of the same sins at that point (I think Satou pen'd both her friend and their teacher during their "final" dates. So teacher prob got his virginity). After all, if he's gonna agree to the reset there's no reason to hold on to his virginity.
If they chose not to reset, Rikka promised not to have penetrative sex with other men going forward, and she'd be ok with Satou continuing what he had with the other girls. It's still for the better that they had the reset though, the only happy ending which was only possible because doing it through Koyuki negated the "compensation" from being paid.