In terms of the action:
* Abstainer: Someone who refrains from sexual activity or seduction.
* Chaste: Someone who is pure and morally upright in their sexual behavior.
* Loyal: Someone who is faithful to their partner and resists temptation.
* Temptation resister: Someone who actively resists seductive advances.
In terms of the person:
* Pure: Someone who is innocent and free from sexual desire or experience.
* Virtuous: Someone who has strong moral principles and avoids sexual immorality.
* Loyal: Someone who is faithful to their partner and resists temptation.
* Innocent: Someone who is naive and unaware of the ways of the world.
In terms of the effect:
* Repulser: Someone who repels or rejects advances.
* Detacher: Someone who distances themselves emotionally.
* Rejector: Someone who refuses to engage in a romantic or sexual relationship.
The best opposite will depend on the specific context of your question.