Well, I meant it in a 'loved one' way rather than a pairing, because Voldemort, incapable of love or not, shows a bit more affection for Nagini than these paranormal YA wretches show for their girlfriends. But... er... as a pairing? Probably yes. XP
And in Fire Emblem, there's certainly a few cases of men going batshit insane over their wives' deaths and turning to unholy magics to bring them back... so that sort of counts, even if they weren't villains at first.
no subject
And for a general list, here's the TV Tropes pages for romance and friendship, respectively:
http://tvtropes.org/pmwiki/pmwiki.php/Main/UnholyMatrimony
http://tvtropes.org/pmwiki/pmwiki.php/Main/VillainousFriendship (the Type 1 examples)
And in Fire Emblem, there's certainly a few cases of men going batshit insane over their wives' deaths and turning to unholy magics to bring them back... so that sort of counts, even if they weren't villains at first.