Apart from harems being an in-game reality – going so far as being able to stumble into one's own given a modicum of infidelity – having Olga stay alive isn't as simple as you make it out to be: it requires either giving up said possible harem
or not being in a relationship with anybody else. There is no 'right choice' in the latter's case. Acting like people made the wrong decision by picking Emily, or Sofia, or Rachel, or Nina, or Anne, or Maxine, or Grace, over Olga is a tad rude, in my book. Especially given you prior post:
There's no bug to fix here. Lily's arc is a deliberate design decision by the developer. You (and apparently Vidal) simply want it changed – just like some of the people being with other girls would like for Olga to stay alive. By your latest reasoning 'breaking up' (remember: not your girlfriend) with Lily can be avoided by not getting involved with her in the first place (possibly having her end up in this universe's version of Azkaban). 'Simple as that.'