you cant see stress it during the sex, it will only say "<slave> has become <mildful><completed> or is at break down point (something like that). The best way to get ride of stress is using invigorate AFTER you get Magic Affinity to over 10 (after some point, it will lower stress when you cast it, no sure how much MA its needed.. at least 8 I think), when in 12 it will go down by 18 every time you cast it. You can aways cast dream in case the stress is too high and you are out of options.
Lust will show up after arousal has gone up... not sure if it will ever go down during sex, I just got used to getting ride of it by raping defeated enemies. Outside you can click in the portrait to see both, inside the mansion I usually use mindread to see these stats.