To add on to what
vandal.h said:
While all the sex scenes are optional, you don't get any say over her attitude during the scene itself. However, if you read the text leading up to the choice you will usually have a pretty good idea of how it is going to go down and can factor that in to your choices.
As for Jezera, in her NTR path she is ostensibly trying to help Alexis repair her relationship with Rowan by teaching her to be more sexually liberated, so Jezera isn't humiliating Rowan. However in reality Jezera is wrapping Alexia further and further around her finger and by the end it is pretty apparent that Alexia isn't thinking about Rowan at all anymore.
If you are looking for "safe" people for Alexia to sleep with you might want to let her to get to know Greyhide and X’Zaratl, and to have work in the breeding pits to meet Sil and the maid Job to meet Mary. Jezera is also fine as long as you don't start her NTR path (keep Alexia's relationship with Rowan high). Also most of the one off scenes you'll find here and there than are fairly safe.