It's really difficult to side with one side or another here...
From one side we have a...monster (or a spirit?) in love, she is pure meaning that she don't seems to know the difference between good and evil, but she instinctively know she want what is better for the object of her love and want him all for herself, nothing else.
From the other side we a normal human that for the first time is before something that cannot be explained with logic or science, he kwow that she is different and that she can be REALLY dangerous, he is afraid, as all normal human would be, and is at his wit's end. Now he discover that his good friend is dead in a gruesome and innatural way and for all he know there is only one supernatural being....
As a human i don't really know what i would have done myself, still i really hope she isn't the murder.