Pretty sure that one depends on how much Sammy has been slutting things up. I mean, Dani is hardly going to ask some church-going virgin to keep watch while she goes whoring, no matter how friendly they are. I do not know whether is it locked behind one or both of the Slut/Whore perks, or just a soft check to see if Sammy has been around the block a few times.
Similar to the whole
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And again, and on a general note, I feel obliged to stress how much these things are part of the game's DNA.
This is not a list of quests to check off. This is not a game that holds your hand every step of the way. This is not a game where you can expect to see every bit of content in a single playthrough.
What it is is a game that expects you to – and rewards you for – trying things. A game where playing differently means that different things will happen. Or not happen. And yes, it is a game that at times does not explain itself clearly, or at all. Much like life.
Now the good news, as mentioned a few days ago, is that an official guide/walkthrough/whatever is in production, and will be bundled with the game once ready. And some things will be tightened up and explained better in-game as development progresses.
And for those who don't want to figure things out by trying different things, and don't want to read a guide when the game fails to hold their hand tightly enough? For those there are literally thousands of other games out there that will do just that. We do not all have to enjoy the same thing.