Board Thread:Spoilers!/@comment-26225812-20150611110107/@comment-6175354-20150617135547

Eskaver wrote:

Well, the problem with that is......Mal is a powerful sorceress and likely wouldn't be seduced or forced to sleep with him. Arthur probably became controlling because she had eyes on another man.

Lily implied that dragons are "loose", so to speak. It would not take much, for that one-night stand to happen.