I went back to read the whole story from start again ...
In act 64 (yacht) there is following dialog between Tasha (M) and Christine (A) :
label V14Act64:
...
M "And besides, this morning I saw them sleeping in the same bed!"
...
A "I don’t see what’s so bad about that, they used to sleep together all the time when they were younger."
M "Well yes, but this seemed different."
M "I’ve also seen them sneaking around at home."
M "Once, I got home and they were all flustered on the couch…"
M "And the main reason I wanted to visit you was so I could get your opinion on all this… You’re the only person I can trust with something like this…"
A "And here I thought you just missed me!"
...
A "Who cares even if they {i}are{/i} doing something?"
M "How could you say that?!"
A "They are young, full of hormones and just want to have fun."
A "That’s just what they are like, and I don’t see anything wrong with it."
M "They are [rel.br] and [rel.si] for god’s sake!"
A "That only really matters if they are gonna have babies you know…"
M "So what are you saying? I should just let them go at it?"
M "Hell, if that’s the case, why don’t I join them too? It’s just having some fun!"
A "That’s the spirit!"
It took dev another 147 acts (or 37 monthly updates = ca 3 years) to finally have Tasha "join them" and "have some fun".