You are correcr there is a real distinction between when you have sex with someone you love and then just having sex for the lust/enjoyment but sometimes you can have both.
Just not with your sister haha
But an open relationship is certainly not for everyone.
I have found it odd how so many people will happily cheat on wives and partners etc instead of having a conversation about monogamy and if it actually works for them and in their best interest in the long term.
To have a relationship without sex for a partner would be like a prison sentence for some but yet the same partner who denies that intimacy won't allow for their loved one to get that from someone else in a trusted/respected way...