Alright... a million years old update on the experiments ive conducted with the "lets have sex" call out:
The call out is utterly borked, and breaks instantly (bugs out) once a certain condition is met.
As ive mentioned in my previous research posts, you cant be interrupted or competed against/over while in a sex session resulting from this call out. Your partner also wont interrupt you, regardless of their virtue. All good stuff... except until it breaks.
The bug manifests, when some other NPC has over 21 love count with you (and was made a sex friend of), other than the first NPC youve bedded/turned into a sex friend.
If you play mono without other relationships, and no other sexual partners, the partner youve made sex friends with will always go for you, when you use the "lets have sex" call out (or their relationship partner, if they have one and theyre present on site - depends on love count difference). But if two or more NPCs have over 21 love count with you - it breaks.
The initial partner you would love to fuck will always turn away in a random direction, even though (according to QtEdit) theyve accepted the call out. This doesnt make them completely useless to you, as you can still extract sex from them in an orgy (or by forcing them...), but the call out in this case has to be made by someone else. Lets say youve stumbled on an orgy, the high virtue chick is just watching the depravity. You cant use the call out to have sex, since it will do nothing. You have to wait for another NPC to use it, which will then direct your target to you. Oh and, obviously, no other sex friends of yours need to be present at the time... which makes the window of opportunity all the more narrow.
Its strange, but it is a bug. Blame Illusion/Ill-games.