Love Bites by Taryn Quinn

It aches, it burns…sometimes it even kills.
Vampire Kellan Barstow is tired of watching his best friend Lucas Phillips pine after his one true mate. Though he’s jealous that Lucas found his before he found his own, he wants him to be happy and hopes to spur him on to make a move toward his chosen human, librarian Emily Yost. But Kellan’s sick of Lucas’s moping and decides one thing will convince Luke he needs to act.
Sleeping with another woman.
Except when Kellan and Lucas sleep with Sydney, a woman Kellan has flirted with for weeks, things quickly spiral out of control. Because Sydney may be more than merely a woman, and Kellan’s feelings for her soon go way beyond desire. Before long, Kellan and Sydney and Emily and Lucas are caught in a dangerous web of lust and love. And this love may do more than bite—it might end them all.