Well, hmmm. It's possible I've never had an affair couple making out in the hot tub either (my game is too tame!) so I can't speak to that either way. But now I'm very interested to know just how many hot tub make-out animations there are.
Attraction (boltage), which is all "the hotter they have it for one another" could mean for purposes of objective game functioning, as opposed to subjective sense of how "hot" a sim couple CAN have it for each other, doesn't seem to be a determining factor, though. My three-bolt YA/adult couples - married or not (to rule that out) - don't use the "hotter" animations the one-bolt teen couple I saw the other night did. So I'm still thinking it's age-related, although now I've got to try an affair to if I'll see what you've seen.
Your "They were going at it for hours." makes me wonder about that, because I can't imagine one couple's make-outs being longer than another's, aside from difference in length between different animations. I could certainly be wrong, but I'm pretty sure make-outs are preprogrammed to be a set length. I figure "going at it for hours" is either a figure of speech on your part, or they were stacking up several make-outs that looked like one long one.
If that sounds snarky, I don't mean for it to. It's just that I've got what I suspect is a tetch of the OCD, can be very literal, and am a stickler for specific, deliberate observation and testing before I can comfortably go with what someone else says is true when I haven't seen it for myself.
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