The dialog in question is triggered by Ramazith himself walking towards you and asking why you remain in his home. The purpose is to provide a way to liberate the nymph.
The problem is that the dialog seems to only be triggered by leaving and reentering his home several times. The dialog itself doesn't make sense as he is asking why you remain in his home an not why you have returned; also when asking why I returned doesn't necessarily make sense since it doesn't always trigger.
I was able also able to trigger him speaking to me by casting a spell like "Protection from Evil" or "Summon Monster" in his presence.
Although not a bug per se, it is very difficult to reestablishing this dialog and it would make more sense for it to occur by your character talking to him. The expected behavior for this situation would be to trigger the dialog by speaking to him directly. Or to always have it trigger when reentering his home the first time (and not seemingly at random).