User blog comment:Leadp1pe/Is a Succubus Faithful?/@comment-24851346-20140618134046/@comment-24934423-20140619035241

Nah, Wilmarina was a special case. She loved "you," but had to suppress those emotions in order to be Wilmarina the Hero. Emotions don't like to be bottled, especially love. When she was turned into a Succubus, those built-up feelings were let loose, and she became exceedingly obsessive over being with "you."

Basically, it's the thing that Elves end up having to go through. ( =w=)/

The Demon Lord's husband is the first Hero the Order sent out to kill the current Demon Lord. Instead of killing her, the two of them fell in love.