Haha i mean come on, thats like the worst kind of "slut-excuse" ever, i really cant this "Uhhh we did looots of romantic and intimate stuff with each other but things were "undefined" and we werent exclusive" serious. Its the worst kind of copium excuse to make these avn protagonists likeable and the girls understanding.
I mean just turn the genders around, how much would you "like" a LI who keeps her options open and has like 2-10 other guys on the side because "the relationship wasnt defined yet yo". Not that much i imagine if youre not a ntr lover
Youre right, its not easy to create a harem in a setting like this (without fantasy or apocalypse or smiliar events making it more logical) in a logical way but just ignoring it until everyone is magically happy and so in love with the MC who fucks every girl with two legs is simply not a good solution no matter how much we change terms and "undefine" things lol
The problem is as deeper the bond at the time of the unraveling of the cheating, as more it hurts (or it should if feelings are really involved), its a relationship based on lies and dishonesty which is the worst kind of fundament for any kind of relationship but even more in case of a harem (or poly relationships) where communication is utterly important.
The MC being this dense in a social sense is imo kinda the chance in the avn, Lexi could (for example) be the one pushing the harem idea as hes way too clueless himself anyway and his romantic antics are as you said unintended - which i love by the way - this is BY FAR the best virgin MC ever lol, the dev managed to create a virgin who doesnt look/seem pathetic because of it, its very fun lol.