Why do soul mates exist ?

what would one say about he power of witchcraft and dark magic? I have a friend that more than likely is under the influence of black magic with out even knowing it. His energy is always low and its like something moves him to do bad things for no reason

I tried to tell him but he doesnt believe me simply because he cannot come to consciousness about it

I have known this person a while and hes been strange and has not been himself for a long long time now.

He is a good good friend of mine and of course i care.

How would I go about helping him out?