Regarding this, about a week ago I encountered something that I'm not sure if it's a bug or it's intended but I just forgot to put it here till now:
Python:
if holly_trinity == 2 or lena_holly_dating or (ian_lena_pure and ian_lena_3some == False) or (ian_lena_couple and ian_lena_open != "lena" and ian_lena_open != "ian"):
jump v13emmadateend
So that confirms what you said that if relationship Lena/Holly or trinity, sex with Emma doesn't happen. Also if Lena and Ian are in a serious relationship and didn't already have a threesome with Louise, sex doesn't happen either, which makes sense. The part that I'm not sure if it's a bug is that if you have an open relationship since the beginning (ian_lena_open = True), sex doesn't happen. You need to have the relationship opened during the beach trip crisis.