Honestly I think you're overthinking it. My advice is to take a step back and ask "What am I making content for?" If your focus is on making new scenes for the elf boy then put your attention on that. If helping him without sexing him is just a role-play friendly way of asking him to leave, then it doesn't matter where you send him. Just write a couple sentences where the player suggests a logical place and make it clear the elf won't see them again. You don't need to attach a quest to it or go any further with it.
If you're worried about undermining a pure player I have a few suggestions (though personally I recommend the first one):
1) Easiest one: just put in a line saying that the Elf handling it themself will take longer, or just be more difficult than if the player helps. That's all you need.
2) More labour intensive version: lean into it and make it the crux of a corruption scene. The Elf and Champ both realize they're just making excuses, screwing won't actually help, but they'll take any chance to fuck each other even if it'll ultimately make them more corrupt in the long run.
3) Have a companion deal with it. You can take that as a chance to write scenes with the party members or as a dismissal, like sicking one of your companions on the Elf priestess or getting someone else to milk Brienne.
Ultimately, you should focus on writing the scenes you want to write. Worrying about stuff outside that will just stress you out and burn you out. If you decide later that you have a fun idea for a quest or scenes after the player sends him away (say he becomes the village whore, or accidentally corrupts the cloister) then you can always update the mod then.
Looking forward to reading what you come up with.
