I think the sharing theme just never crossed her mind at all. GGGB had the open relationship route but it just had end up with FMC cucking the shit out of her bf while he watches, no indication of him liking it since it wasn't his idea at all. Similar thing happened in ORS as Lena had to cheat first or both of them cheating to get that relationship open up, even the talk about Lena bringing another man for them to have a mfm threesome pretty much required her being a slut and Ian having cuck_points.
EK games had always heavily leaned towards the cheating fetish because every chapter has tons of choices and variables and most of them had to do with cheating. Just play a vanilla playthrough between Ian and Lena you will see a really typical sweet young lovers where the drama happening around them had nothing to do with them, while you are doing that route you will see how many choices you are given in a single chapter for them to start cheating and turn the ian_cheating/lena_cheating variable to 1

. Every time a girl flirts with Ian or another guy flirts with Lena you will be given a choice to cheat on their relationship, easily.
And also thanks to our wholesome community here, the vulgar reverie thread got locked.