A combination of the words Obsessed and Assasinate.
Best used to describe somebody who is so in love that they cannot stand the idea of anybody else getting close to the object of their desire. They can become so consumed with jealousy that they often fantasize about killing said persons.
'Bob loves Kelly so much that he dreams about killing any other guy who tries to gets near her.'
Bob is showing obsessinate behaviour.
Bob is an obsessinator.
Bob thinks about commiting an obsessination.