You know... come to think of it, I haven't seen that one either? After a quick look at the requirements to trigger it, I think I see why. First of all, for it to come up, you just have to make a couple random rolls that leave you at about a 5% chance, and then there's one last stat requirement that lowers the odds even more-- your girlfriend has to fail an addiction check for the event to actually trigger, (her addiction_need has to be higher than a random roll between 50 and 100.) So, she has to build up enough of a need that she fails that check, without her getting her fix anywhere else, earlier in the day.
That's kind of tough to set up. When her addiction_need is that high, there are so, so many other events that also start to trigger where she can get her cum fix, and you have to avoid all of them until that base 5% chance comes up. (And the addiction information widget seems to be broken in the current version, so... it's pretty tough to even figure out when she *might* be able to fail that check.)