My Soul to Keep (Soul Screamers #3) by Rachel Vincent

Kaylee has one addiction: her very hot, very popular boyfriend, Nash. A banshee like Kaylee, Nash understands her like no one else. Nothing can come between them.

Until something does.

Demon breath. No, not the toothpaste-challenged kind. The Netherworld kind. The kind that really can kill you. Somehow the super-addictive substance has made its way to the human world. But how? Kaylee and Nash have to cut off the source and protect their friends—one of whom is already hooked.

And so is someone else…