The Secret Art of Failure Series by H.B. Kurtzwilde

Kourt Crowe, the last remaining Servitor assassin, also a shape-shifter, lives to restore the lost golden age of the Fellowship of Servitors. His first husband died over a century ago, and, since then, he's been fighting his battles alone. This next battle may be more than he bargained for, as he finds himself head-to-head and body-to-body with a promising, but troubled human student... moreKourt Crowe, the last remaining Servitor assassin, also a shape-shifter, lives to restore the lost golden age of the Fellowship of Servitors. His first husband died over a century ago, and, since then, he's been fighting his battles alone. This next battle may be more than he bargained for, as he finds himself head-to-head and body-to-body with a promising, but troubled human student. Evicted from his college for broken vows, self-described five-star hottie Kato Giovanni isn't ready to hang up his dreams. With his razor-sharp mind and native genius for theoretical mathematics, he convinces bad-ass Master Kourt to take him on as a student. He wants to learn. Really, he does. But he can't help testing all of his teacher's boundaries. less