There is a general expectation that YA novels depict safe sex. An exception would be if you’re intentionally showing characters being irresponsible or naive about safety and pregnancy. I do hear your artistic rationale for avoiding that down-to-earth detail among your otherworldly revelations. I’ve got an idea: Early in the scene, your character could put a condom in his/her pocket in anticipation of the upcoming encounter. That way, when the bodies get down to business, there’s an implication that the condom mentioned earlier is being used now, even though you don’t call it out specifically. The safe sex message is accomplished, and your complex, highly stylized scene is unmarred by a clunky condom call-out.