Yes, by the end of the movie he's going all-out Devil on the girls, using magic and shit to harass them. But he was kind of pushed into it.
So what went wrong? A few things. When a nosy neighbor decides to talk smack about the Devil, he suggests the three women curse her with the misfortune of vomiting cherry pits. So, it's more of a prank than a curse. It's mildly gross at worst. Unfortunately, nobody involved had any idea that their victim's psychotic husband would freak the hell out over her illness and beat her to death with a fire poker. That's not the sort of thing you can predict, even when you can fly.
Pokers: For when your insurer refuses to cover mental health problems.
So the lady dies and our three witchy women break their deal with the Devil. They turn their backs on him. And if you think breaking up with your first high school love was harsh, try breaking up with Beelzebub, who takes it really, really hard. He doesn't just smirk and skip town for some bigger, sexier orgy elsewhere. He's heartbroken.
So, he takes supernatural revenge on them (messing with their heads, that is -- he causes no actual injuries). But listen to the guy, he sounds borderline suicidal.
"What do I want? Christ, what does every man want? A little affection. A little trust. Goddamnit, everything I did, I did for you."
Yet we're supposed to be cheering when, in the end, the witches curse the Devil to death. So, "murdered" is probably the better word here. Oh, and that's after he got each of them pregnant. So they murdered the father of their sons, who left them his mansion (which they happily live in once he's dead) and wealth. All in all, it's a pretty crappy way to treat a guy who only asked for a nice Pfeiffer/Sarandon/Cher four-way.