Tasting is giving in, not staying away.
There's no in-between, you either give in or you abstain. Sex with a Succubus is not abstaining from temptation at-bloody-all and you signed the death warrant for Connor which really should have been you but plot convenience.
A Desire Demon is not a succubus. The deal was, allow the demon to survive and return to possess Connor long after the Blight is over. In return, the Desire Demon will give you knowledge, or pleasure (sex), or the love of those around you (+Approval)
The Demon already had Connor. It can't possess the Warden when its bound to Connor. I'm pretty sure you can even ask whats to stop it from possessing the Warden, and it even states "I already have one host.", it wouldn't risk trying to possess a powerful mage like the warden and losing
So no, it made complete sense (Or atleast as much sense as dream spirit sex demon bargains do lol) its not really meant to be a serious choice, its just hilarious to sacrifice a kid just so its implied you bang a demon / have a wet dream, must have been awkward guarding the warden's sleeping body. xD