like you say, i also think trust is not a yes or no. there are different areas of trust. i might trust a friend to safely drive me home while sleeping but i won't trust him to pick me up next week on time because he is a disorganized fuck up.
so i still dont see where sharing sex stuff is a problem because of his cheating if the guy is trustworthy regarding secrets and is probably not leaving you because of your fetishes but happy to finally have some non-vanilla sex
its just different areas of trust
the whole thing also doesn't fit with reality imo. girls have no problem trusting men in many areas of life a lot if warranted while having little trust in their fidelity at the same time.
i dont think the game even presents it like mina didnt share her list with ian because of his cheating, but those who see it like that probably just want to believe in that fantasy that a guys fidelity is the main factor of a girls overall trust and willingness to do naughty shit with them
aside from keeping secrecy because of the public consequences you mentioned, its not like sharing some fetishes is climbing the K2 in a team of two
iirc i think the game presents it more like somebody else here wrote: girls try to hold on to their cultivated image in the relationship with their boyfriend for different reasons (mostly benefits and avoidance of risk), but when they meet somebody new to fuck around with there is not much at stake, so they suddenly are willing to do things they'd never agreed to with their boyfriends/husbands
I think that's a really reductionist view on female relationships. It makes Mina out to be a cynical emotional mercenary, 'cultivating' an image for 'benefits'. It reduces her relationship to being merely transactional. Sorry, but I see enough of that toxic thinking with the libertarian crypto-bros (e.g. everything in Web3, including social structures like DAO's, are built around financial transactions; it's future is the financialization of everything).
There is a difference between someone who is very sexually permissive, who's unafraid to let their freak-flag fly and damn all the consequences; and someone who fears the consequences of others learning about their sexual preferences. The former might not require a high level of trust with a sexual partner to get into the really kinky shit. But that's hardly universal, and certainly isn't the typical or the default response.
Do you perhaps live outside of the United States or Canada? I know that western European nations tend to be more liberal in regards to sexuality, but both the US and Canada skew heavily in favor of sexual conservatism and repression. We're all about blood, guts, and gore; but heaven forbid if anybody sees a lady nipple free in the open.
So yeah, having a terribly untrustworthy partner (based on infidelity or not) is a perfectly reasonable explanation for not sharing their Taboo Kink Bucket List with said untrustworthy partner; for all of the prior reasons already stated. If you can't trust your partner to maintain their half of a commitment to a monogamous relationship, how are you supposed to trust that they won't use your darkest secrets against you? That they won't disregard their respect for your privacy in the same way they could disregard their fidelity to your relationship?
That you don't seem able or willing to bridge the connection between 'relationship fidelity' and 'relationship trust' and how the two are codependent, is honestly quite baffling. Not everyone needs a high-trust environment to let their freak flag fly, but for those who do, suspected infidelity is a perfectly reasonable reason to erode trust in another or their relationship. Healthy relationships require trust. Mina might have already been heavily invested in her relationship with Ian (again, sunk cost fallacy), but without sufficient trust, she evidently wasn't comfortable investing even more (e.g. her Taboo Kink Bucket List) into the relationship in the case that it did collapse.
Trust is a central theme of the narrative. Edwin can try to both cultivate it with the carnations, or abuse it for his own gain (e.g. his first encounter with Rosalind). Mina's relationship is a way for the writer to explicitly highlight how trust can be eroded and betrayed, and the consequences of those actions. It then becomes not just an object lesson, but gives Edwin the opportunity to potentially betray the trust of Mina and Hana, the consequences of which have yet had the time to play out.