Shades of Dark by Linnea Sinclair

With a killer targeting human females and a renegade gen lab breeding jukor war machines, Chaz and Sully already had their hands full of treachery, betrayal—not to mention each other. Throw in Chaz’s Imperial ex-husband, Admiral Philip Guthrie, and a Kyi-Ragkiril mentor out to seduce Sully, and not just loyalties but lives are at stake.

Before her court-martial, Captain Chasidah “Chaz” Bergren was the pride of the Sixth Fleet. Now she’s a fugitive from the “justice” of a corrupt Empire. Along with her lover, the former monk, mercenary, and telepath Gabriel Ross Sullivan, Chaz hoped to leave the past light-years behind—until the news of her brother Thad’s arrest and upcoming execution for treason. It’s a ploy by Sully’s cousin Hayden Burke to force them out of hiding, and it works.

When Sully makes a fateful choice, changing their relationship forever, Chaz must also choose—between what duty demands and what her heart tells her she must do.