Bad boys always seem to get the action in romance novels. Why is that? It’s because they have reservoirs of masculinity just from being the anti hero.
But all that darkness has a price. Your author can’t get confused about how far is too far. Anti heroes can lose the hero part very easily. The most important factors to avoid are:
Cruelty. Anti heroes cannot cross the line into irretrievably cruel. Don’t kick a puppy. Don’t mistreat the heroine, and, if he does, he better come round to sorry, or the reader will be done with him.
Irresponsibility. Anti heroes are still heroes. There are a few dings on the hood, but the engine fires up fine. That’s the point. Your AH can’t be a ditz or a loser. If he’s supposed to help her move, he needs to be there. If he’s saving her life, he’s gotta be larger than life and eager to help.
Know the Lines. Men need to know where the lines are in real life for sure. Why do we so often try to remove those lines in fiction? Bondage has rules. S and M has rules. You have to know those rules. No still means no in a dark romance. Never let a AH forget why he’s there. He’s in love with someone, and that definition leaves no room for crossing boundaries and acting like a bruiser.
Dark romance is a favorite of mine as a reader, but I find it hard to write. It requires a willingness to take characters to pretty dark places. Some are killers or bad guys who find a reason to reform.
Mr. Rochester of Jane Eyre is a classic example. He attempts, not just bigamy, but he tries to lure Jane into bigamy, unapologetic at first. It takes a near death experience to really get the point across.
Romance has rules. It’s important for a writer to learn those rules. The first rule is always love one another, even if you’re not the best at it.