Coming Undone by Lynn Hagen

Jonah has known since he was four that Cole was his. He’s loved his mate even before he knew what a mate was. A formula that Dr. Sheehan created saved Jonah’s life, stopped him from dying at such a young age. But now that same cure is working against him. While Dr. Sheehan tries to figure out what is going on, time is running out for Jonah. Frustrated that Cole is away at college and not there for him, Jonah takes off to Lucky Clover to get his mind off things but ends up in the trunk of his enemies.

Cole has been fascinated with medicine since his mate was dying and needed a miracle. Cole’s healing blood provided that miracle. But when he gets called home under mysterious circumstances, he’s blown away to find out that Jonah has become an Ultionem bounty hunter. Worse, Jonah is dying, and now Cole must find a way to save his mate so he can have his forever with the only man he has ever loved.