Yeah Yara in case sees absolute nothing wrong with the ideal of sleeping around because Succubus, hell even the thought that someone would possibly be upset with that does not occur to her for a bit but most of all she is Simon's first slut, hell it is the exact same reason she encourages Simon to sleep with pretty much anyone even those not in the relationship, hell no difference in using her magic to lust someone up to further their goals or using her body
Basically Swinging is the normal relationship of succumbs where they will be together but will fuck other men or women as they see fit because sleeping with people is not really far off a handshake concept, this is quite well
It the same reason why Naill thinks Robin and Simon starting relationship is messed up because Incest is a needed and healthy part of a growing kids relationship with their parents
Also the reason she goes full Rage power vs the incubus idiot supreme where he does intend to NTR and Yara wants none of that and yeah NTR is specify taken away by sleeping with, you can in theory have another women do it but well most people go girl on girl is hot and is not therefore the whole I love this girl now more than you because they are better than you in sex, so fucking other dudes or women by itself in not NTR, NTR is them going I love this person more than you because sex with them is so good
like the closest thing to actual NTR is the Empress and her initial relationship with Simon and Yara when she straight up takes them for her own
also it has Swinging aka Swingers are couples or singles who choose to have an open relationship, allowing their partners to have sex with other people, so just from that tag you can expect that an other man or women fucks the love interest and/or main character
TL: DR sleeping with other men or women is just swinging or cheating depending if it is an open relationship or not, NTR is stealing a lover through sex
Cheating is a tag you can more easily argue since Yara has not really though to talk about it due to culture differences since that could apply but then again Simon never brings it up and he was there the first time Yara used her magic and maybe her body to make someone balls blue to get information
Identifying with a character means feeling an affinity toward the character that is so strong that we become absorbed in the text and come to an empathic understanding for the feelings the character experiences, and for his or her motives and goals, so em your supposed to understand what Simon is thinking or feeling